How to trigger an event in a view control from a ViewModel

Hi,

I'm having a problem where my DataGrid (bound to an ObservableCollection and having CauUserAddItems=true) relies on the event RowEditEnding to update the NewItem row to display a custon 'click here to add a row' message like so:

private void ExportTargets_RowEditEnding(object sender, DataGridRowEditEndingEventArgs e) {
	IEditableCollectionView iecv = CollectionViewSource.GetDefaultView(
		(sender as DataGrid).ItemsSource) as IEditableCollectionView;
		if (iecv.IsAddingNew)
		// using invoke/idle causes a wait until after the NewItemPlaceHolder is added
		Dispatcher.Invoke(new DispatcherOperationCallback(SetEditingNewItemTemplate),
			DispatcherPriority.ApplicationIdle, sender);
		e.Row.HeaderTemplate = null;	// reset row header
}

public object SetEditingNewItemTemplate(object arg) {
	DataGrid dg = (DataGrid)arg;
	DataGridRow row = GridHelper.GetRow(dg, dg.Items.Count - 1);
		if (row.Template != _newRowControlTemplate) {
		row.Template = _newRowControlTemplate;
		row.UpdateLayout();
	}
	return null;
}

The problem is that the row also contains a browse button, which updates the Data Model directly (i.e. not thru the grid control).  Since the Collection is Observable and the binding Mode=TwoWay, this does update the grid, but the RowEditEnding event never fires (since it never began in this scenario), so the new row teimplate is never updated.

I know the ideal solution would be to port the code-behind to MVVM, but the proper events don't seem to be available from within the ViewModel.

So how to I either inject this event from the ViewModel into the view control so the function is called in the proper context or otherwise somehow directly update the row Template?  Right now I'm tangled up in SyncronizationContext and other issues that prevent the direct approach.

Thanks in advance for any help...