Pokerus is based on a virus, but real viruses mutate DNA, not your effort.
So, just make Pokerus give some IV boosts. It's rare, so it won't effect 99.5% of games and the majority of Pokemon will still be individuals. Players who want to metagame can trade online for Pokerus and get perfect min/max'd Pokemon more easily. Win-win --- Not changing this until something impossible happens Started 12/02/12