I have not looked at your full code (sorry) but I believe you cannot do what you ask (ie call controller method from somewhere else) without HMVC or similar. (I am not 100% on this though)
However there is no reason why your callback in, say, controller A, cannot call a common function (say 'common_callback_function') from a model or a library to get a result, just like any library or model call works. It is just a function after all. Then you are free to reuse that common_callback_function in any other library, or from where ever you want. Keeping everything DRY.
I hope that makes sense.
Paul.
