I'd have him studying, class room prep type stuff and working in the gym and on mechanics. Near the back half of this season I'd have him running some 2nd string offense at practice. He'd play almost the entire preseason next year and he gets some #1 reps in training camp. You let him compete for the #2 spot and if he's even close to Rush you go with Lance at #2.
You monitor him for the year and give him 2nd team and some 1st team reps in practice. You play him in any blowout, ahead or behind, and probably prepare a package of plays for him on gameday.
If all looks ok, like someone mentioned earlier, you give him the Jordan Love type prove it deal. He's not going to get much better than that type of offer. It's not out of the question to go this route with a guy with that potential. He wasn't a failure in SF, he was just unknown potential and they went with the more known commodity. There is a decent chance he really is a top 10 draft pick at the QB position. He could flop but it's nuts that people are *****ing that we traded a 4th for him.