OP, based on what you've said, I'd recommend against going on Mummy, the Simpsons, Rip Ride Rockit, Transformers, and the motion seats at Despicable Me (there are stationary seats at the front so he can still see the 3D movie if he loves the Minions). Transformers and Despicable Me would be possible, but I'd recommend you ride them first to see if he really really wants to try the motion part.
Twister, T2 (assuming the machines wouldn't scare him ... it's some pretty convincing 3D combined with live action actors that go in and out of the screen and run around the theater), the play areas of Fievel/Barney/Curious George (the water slide and roller coaster there would be a maybe), and Shrek 4D would all be fine for him, as they are shows.
ET I wouldn't see a problem with (as I said, he can also remain in his chair instead of transferring into the "bike seat"), same with Disaster (it gives you a few good bumps up and down, but when I worked there I saw some kids with some pretty severe balance issues that rode it with no problem, and had a *HUGE* smile on their face when it was over), and MIB (again, depending on how he handles spinning; it's mostly turning the car to re-orient you towards stuff to shoot, but there is one point where the other car can shoot yours and make you spin unexpectedly, and you get a few good spins at the end when you go under the bug).
At IoA, he'd definitely be OK on One Fish and Caro-Seuss-el, Cat in the Hat is another maybe, but he can stay in his chair on all of them. The High in the Sky Trolley he would have to transfer to the ride, but it's a gentle ride and you sit next to him.
Poseidon and the Sinbad show are just shows, he'll be fine in each (and Poseidon is worth it just for the water vortex ... but there is a "battle" at the end that combines action on the screens with water and fire effects in the room with you, which can be scary sometimes).
Harry Potter will probably be the biggest challenge. If he loves the books, he'll love wandering around Hogsmeade. But the two big rides there, Forbidden Journey and Dragon Challenge, will be no-gos for him. He might be able to do Hippogriff if he can handle kiddie coasters elsewhere (Barnstormer at MK, Shamu at Sea World, Grover at Busch Gardens, etc.).
River Adventure is mostly a sedate ride, but it does have one drop at the end (similar to Splash Mountain), and you're sitting right next to him. He'll be able to enjoy the Discovery Center and most of Camp Jurassic; Pteronadon Flyers would be iffy, he'd be sitting in a chair by himself with only a seatbelt, you'd be right behind him but unable to reach him most likely.
Bluto's Barges is a river raft ride, but it's bumpier than most other ones I've been on. Ripsaw Falls is a fairly typical log flume, but has a pretty steep drop at the end, so it would probably be a skip it as well. He'll have full access to Me Ship the Olive play area, and can use water cannons to shoot people on Bluto's.
Spiderman would again be a maybe; Doom and Hulk would be no. Storm Force would be a possible, you do control spinning somewhat from your pod. But if he loves the comic book characters, it's definitely the place to hang out for pictures/autographs, like Bearshouse said.
He wouldn't be able to do everything, but there is still a lot he would be able to do.
Thanks again.
