When I applied for my dd6 I thought the same thing. She was ahead, like you describe, but nothing "prodigious". I too, was worried about there not being anything "out there" to put on the application. I agree that if you write the activities you describe as well as have the tests to back up his ability you will be fine. They accepted my dd without any one "special" thing that she does. I guess she's just well rounded and that's ok too!!!!
Good luck to your son!

Laura