Speaking purely off of watching one pre-season game I would say the "out of the box" idea is to keep Mannion on the team. 3 yards passing in the first half. wow.
I liked Mannion coming out of college... I'm not sure what I saw tonight. Anyway, chances are they'll give him at least a few more games... But if he doesn't improve I will be holding a torch and pitchfork, probably along with some others.
RG3... I don't know. I have reservations but maybe a 1 year deal would be OK. To be honest in this offense most average QB's are going to be OK. The QB will have protection and a running game and receivers who run good routes, with a solid OC... Keenum, Shaun Hill and Nick Foles would be OK in that scenario. And probably Mannion would as well.