Joe just posted an interesting blog concerning ways to get rendered data into the controller. While I don't agree 100% with his solution, I don't have a better idea right now. ;)
That being said - I should point out that there is an API to get view data in the controller, but it does not work well and will (most likely) be removed from Model-Glue. I'm talking about the getView() method of the event object. I had trouble getting it to work right and after speaking with Joe, I'm simply going to remove it from my code and attack the problem from another route.