Change EditableObject behaviour on WPF Datagrid

Question

I have a WPF Datagrid (.NET 4.0) with a list of viewmodel bind to ItemsSource.

The viewmodel exposes the model entity that is builded from a base ancestor class that implements IEditableObject interface.

Every time I edit a cell of a datagrid row the beginedit method of entity is called; I would a different behaviour: call the BeginEdit only when a select the row, so I can discard all row property changes when I call CancelEdit.

How can do it?