Have him take the MSF; that will give him a instant idea of how a 250 will fair under him. (I can’t imagine they’ll put him on anything smaller.)
However, I agree that a 250 is probably not the best idea for someone that big; just he, his gear, and a full tank of fuel may be pretty close to the bike’s maximum GVWR, depending on the model. With that kind of load, reasonable freeway speeds may be completely out of the question.
Given his really a-typical size, his best bet is to tour the dealerships and sit on anything he sees until he finds something he likes that fits. Then, even if he wants used and they don’t have it, he at least knows what to look for when searching around.
Depending on what he wants, a mid-sized cruiser with forward controls may fit the bill, or a dual-sport like the V-Strom 650. I also wouldn’t discount something like a Ninja 500/650 or a GS500/GSX650F. Basically, I’d still aim for something in the 500-650cc (just not a super sport) range for a sport, standard, or dual-sport and *maybe* something just a bit larger in the cruiser category. Just don’t go crazy; his size may warrant a little more grunt, but it’s no substitute for experience.