That's a bit tricky. But you are going down the right path.

Essentially you have a custom controller, that acts as a proxy to the other two controllers (Box and multi) and you are taking the custom actions and using the Box and Multi APIs to trigger the UX behavior you want.

I'm not completely sure which event is missing, but you can look at the unmagnified source code of Box and Multi extensions, to figure it out.

Does that help ?