If he's that big (and I'm sure that'll change), don't let them talk him into the following follies:

-any weight supporting element that involves carbon fiber
-As eden said, wheels with less than 36 spokes. I'll add a bit and say he would do well to go with wider rims that can handle 35C tires or better.
-I would almost recommend he go with upright (e.g. moustache) handlebars. If he's that large, he will find the upright position much more comfortable. He can go with drops later if he's so inclined. Might even be a good motivational tool.