It's simple, have two leagues.

1. Human performance only - no drugs, no implants, no performance boosts. 2. Unlimited league. Take all the drugs you want, when we have them, install new muscles, cybernetic implants, whatever. Go wild.

This way, the real purists, who want to push the envelope of human capability get to do so without having to compete with dopers.

AND

High dollar/prestige sports will fund new and interesting areas of biomedical research. It will be like indy car racing for human bodies.