flat dishes, peroxide wipe once a day...
Have you tried feeding him from a flat dish. That way he is less likely to get his chin in the food. I have also thought I heard some recommendations to wipe the cat's chin at least once a day with 3% peroxide.
You may have a different situation than the average acne and the Vet is the right road to take until it's cleared up. Once it clears, I would switch to a flat dish..... and cleaning his chin often, to prevent the accumulation of food goo!
Keep us posted!:p