iphone - Detect lightweight core data migration

I'm using Core Data's automatic lightweight migration successfully. However, when a particular entity gets created during a migration, I'd like to populate it with some data. Of course I could check if the entity is empty every time the application starts, but this seems inefficient when Core Data has a migration framework.

Is it possible to detect when a lightweight migration occurs (possibly using KVO or notifications), or does this require implementing standard migrations?

I've tried using the NSPersistentStoreCoordinatorStoresDidChangeNotification, but it doesn't fire when migrations occur.