mix aspirin and peroxide until you get a little pastey substance...apply, let dry and re-apply.
theoretically, the peroxide will help open the pores, allowing the salisylic acid (eats oil; see Clearsil) in the aspirin to eat the oil up...
I would be very reluctant nowadays to apply aspirin or any other salicylates topically to a child's skin. Reye's syndrome is a rare but devestating complication of aspirin use in children. I have personally had one 6 year old patient in my care who ended up requiring a liver transplant after having been rubbed with oil of wintergreen (a salicylate containing product) by his grandmother.
Adult use would be OK as far as I know (but I am just a simple country pediatrician and I wouldn't take just my word on that).