You can use mx.processor.subscribe to get changes in objectUpdate for an entity.
To subscribe to an object you can use
mx.processor.unSubscribeFromGUID(this, contextGUID);
mx.processor.subscribeToGUID(this, contextGUID);
this.changeHandler = this.subscribeToChange(contextGUID, null, dojo.hitch(this, this.changeReceived));
See checkboxselector for a complete case.