They have, or had, test seats for Tron set up in Tomorrowland a while ago. Theme Park Express (who is probably a bit bigger than Nate, although at the rate Nate has been going)...tried it out, and while he fit (although the seats didn't have the indicator lights, so you can't know 100%) it looked like a squeeze. Apparently, the standard is that if you can fit Flight of Passage, you should be able to fit this, and there are also a few more traditional seats for the bigger folks.
Granted, Nate's problem is that he's super-athletic....