Okay, first keep a Pokemon or two in your box and bring them out only to infect other Pokemon, then use the Pokerus on an untrained Pokemon for very fast EV training. It doubles the rate of EV gain. You can find which Pokemon yield which EVs on Bulbapedia.
The Pokemon is eventually cured, but as SlickMario stated, the effect remains. However, the Pokemon will no longer be able to infect others, which is why keeping a couple in the box is recommended.