If the masked editor doesn't do that then the simplest way is most likely to use a converter on your binding.

 In your resources:

<local:StripSpacesConverter x:Key="conv"/>

Elsewhere in XAML: 

<igEditors:XamMaskedEditor Text="{Binding Path=stockNo, Converter={StaticResource conv}}"/>

 In code behind:

public class StripSpacesConverter : IValueConverter

    {

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)

        {

             return value;

        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)

        {

            return value.ToString().Replace(" ","");

        }

    }