Controller observer?

I've looked over the Controller API and some of its subclasses (e.g. SpatialTransformer, KeyFrameController) and I don't see a way to observe a controller's status. I'd like to be able to add an observer (some kind of a listener) to the controller and get notified when, say, the animation ends. Can this be done with the current API? I would especially need to observe animations which are imported from 3ds files (SpatialTransformer).