You could programmatically end the edit mode session when a mouse button is pressed over a certain point of the control.

Example:
this.ultraGrid1.MouseDown += new MouseEventHandler(ultraGrid1_MouseDown);

void ultraGrid1_MouseDown(object sender, MouseEventArgs e)
{
    UltraGrid grid = sender as UltraGrid;
    UIElement controlElement = grid.DisplayLayout.UIElement;
    UIElement elementAtPoint = controlElement != null ? controlElement.ElementFromPoint( e.Location ) : null;
    object context = elementAtPoint != null ? elementAtPoint.GetContext( typeof(UltraGridRow) ) : null;
    if ( (context is UltraGridRow) == false )
    {
        UltraGridCell activeCell = grid.ActiveCell;
        if ( activeCell != null && activeCell.IsInEditMode )
            grid.PerformAction( UltraGridAction.ExitEditMode );
    }
}