I have a column that uses an IValueConverter to change the text.  I'm using a style to insert a TextBlock to display this updated text in the cell.  In my first attempt, I made a very simple style, just containing the TextBlock.  As I've discovered, at a minimum, a ContentPresenter named PART_EditorSite needs to be in the style to get editting to work. I've attempted to copy the entire style over from the built-in styles to get the editor to display.  The result is below; both the editor and textblock display at the same time while in view mode.  While in edit-mode, the textblock does remain visible, but it is almost completely covered by the editor.

I copied the style from DataPresenterGeneric_Express.xaml

Here is the style:

    <Style x:Key="StrikeStyle" TargetType="{x:Type igDP:CellValuePresenter}" BasedOn="{StaticResource {x:Type igDP:CellValuePresenter}}">
        <Setter Property="VerticalAlignment" Value="Stretch" />
        <Setter Property="VerticalContentAlignment" Value="Stretch" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type igDP:CellValuePresenter}">
                    <igWindows:CardPanel>
                        <Border
                            x:Name="MainBorder"
                            CornerRadius="{TemplateBinding CornerRadius}"
                            BorderThickness="{TemplateBinding BorderThickness}"
                            BorderBrush="{TemplateBinding BorderBrush}"
                            Background="{TemplateBinding Background}"/>
                        <TextBlock x:Name="Active"
                            Text="{Binding Content, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource StrikeConverter}}"
                            HorizontalAlignment="Stretch"
                            VerticalAlignment="Stretch"
                            Width="Auto"
                            Height="Auto"
                            SnapsToDevicePixels="True"
                            Opacity="1"/>
                        <ContentPresenter
                            x:Name="PART_EditorSite"
                            HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                            VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                            Margin="{TemplateBinding Padding}"
                            Style="{TemplateBinding ForegroundStyle}"                            
                        />
                    </igWindows:CardPanel>
                    <ControlTemplate.Triggers>
                        <!-- HighlightAsPrimary -->
                        <Trigger Property="HighlightAsPrimary" Value="true">
                            <Setter Property="Background" Value="{Binding Path=BackgroundPrimary, RelativeSource={RelativeSource Self}}"/>
                            <Setter Property="BorderBrush" Value="{Binding Path=BorderPrimaryBrush, RelativeSource={RelativeSource Self}}"/>
                            <Setter TargetName="PART_EditorSite" Property="Style" Value="{Binding Path=ForegroundPrimaryStyle, RelativeSource={RelativeSource TemplatedParent}}"/>
                        </Trigger>
                        <!-- IsFieldSelected -->
                        <Trigger Property="IsFieldSelected" Value="true">
                            <Setter Property="Background" Value="{Binding Path=BackgroundFieldSelected, RelativeSource={RelativeSource Self}}"/>
                            <Setter Property="BorderBrush" Value="{Binding Path=BorderFieldSelectedBrush, RelativeSource={RelativeSource Self}}"/>
                            <Setter TargetName="PART_EditorSite" Property="Style" Value="{Binding Path=ForegroundFieldSelectedStyle, RelativeSource={RelativeSource TemplatedParent}}"/>
                        </Trigger>
                        <!-- IsSelected -->
                        <Trigger Property="IsSelected" Value="true">
                            <Setter Property="Background" Value="{Binding Path=BackgroundSelected, RelativeSource={RelativeSource Self}}"/>
                            <Setter Property="BorderBrush" Value="{Binding Path=BorderSelectedBrush, RelativeSource={RelativeSource Self}}"/>
                            <Setter TargetName="PART_EditorSite" Property="Style" Value="{Binding Path=ForegroundSelectedStyle, RelativeSource={RelativeSource TemplatedParent}}"/>
                            <!--<Setter Property="Visibility" Value="Visible" TargetName="LeftBorder" />-->
                        </Trigger>
                        <!-- IsActive -->
                        <Trigger Property="IsActive" Value="true">
                            <Setter TargetName="PART_EditorSite" Property="Style" Value="{Binding Path=ForegroundActiveStyle, RelativeSource={RelativeSource TemplatedParent}}"/>
                            <Setter Property="Visibility" TargetName="Active" Value="Visible"/>
                        </Trigger>
                        <!-- IsMouseOver -->
                        <MultiTrigger>
                            <MultiTrigger.Conditions>
                                <Condition Property="IsMouseOver" Value="True"/>
                                <Condition Property="IsSelected" Value="False"/>
                                <Condition Property="IsFieldSelected" Value="False"/>
                            </MultiTrigger.Conditions>
                            <Setter Property="Background" Value="{Binding Path=BackgroundHover, RelativeSource={RelativeSource Self}}"/>
                            <Setter Property="BorderBrush" Value="{Binding Path=BorderHoverBrush, RelativeSource={RelativeSource Self}}"/>
                            <Setter TargetName="PART_EditorSite" Property="Style" Value="{Binding Path=ForegroundHoverStyle, RelativeSource={RelativeSource TemplatedParent}}"/>
                        </MultiTrigger>
                        <!-- Field.IsFixedStateChanging    JM 01-22-09 NA 9.1 FixedFields   -->
                        <DataTrigger Binding="{Binding Path=Field.IsFixedStateChanging, RelativeSource={RelativeSource Self}}" Value="True">
                            <Setter Property="Background" Value="#AA8DBAEB"/>
                            <Setter Property="BorderBrush" Value="#AA8DBAEB"/>
                        </DataTrigger>
                        <!--SSP 5/27/09 NAS9.2 IDataErrorInfo Support-->
                        <Trigger Property="IsDataErrorTemplateActive" Value="true">
                            <Setter TargetName="PART_EditorSite" Property="ContentTemplate" Value="{DynamicResource {x:Static igDP:DataPresenterBase.DataErrorContentTemplateKey}}" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <!-- DRCA Foreground Hover Trigger-->

            <!-- JJD 4/30/09 - TFS17157 use new IsRecordSelected property -->
            <Trigger Property="IsRecordSelected" Value="True">
                <Setter Property="ForegroundStyle" Value="{DynamicResource {ComponentResourceKey {x:Type igDP:XamDataGrid}, GrayForegroundStyle}}" />
            </Trigger>

            <!-- DRCA Foreground Selected Trigger-->
            <!-- JJD 4/30/09 - TFS17157 use new IsMouseOverRecord property -->
            <Trigger Property="IsMouseOverRecord" Value="True">
                <Setter Property="ForegroundStyle" Value="{DynamicResource {ComponentResourceKey {x:Type igDP:XamDataGrid}, GrayForegroundStyle}}" />
            </Trigger>

        </Style.Triggers>
    </Style>

The only change I made was replacing the Rectangle with the TextBlock.

Original:

<Rectangle x:Name="Active" Fill="{TemplateBinding BackgroundActive}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Width="Auto" Height="Auto" SnapsToDevicePixels="True" Opacity="1" Visibility="Collapsed" StrokeThickness="1" Stroke="{TemplateBinding BorderActiveBrush}"/>

Changed to: 

<TextBlock x:Name="Active" Text="{Binding Content, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource StrikeConverter}}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
Width="Auto" Height="Auto" SnapsToDevicePixels="True" Opacity="1"/>