You also don't want to setup anything that encourages uber-competitive people to intentionally disable themselves to get an advantage. If you allow him to compete and it does prove to give him a big enough advantage I don't think it's out of the realm of possibility that someone could get the procedure done that had perfectly good legs. People do strange things to win.
You're kidding right? Somone would deliberately have their legs hacked off below the knee to compete in a sport without professional level salaries and a financial sponsorship system that's heavily scurtinized!?
Yeah right, maybe if they're truly insane.