You're trying to self treat ear mites, aren't you? As I've mentioned, if he's a well cared for indoor cat, or even indoor outdoor, he really shouldn't have ear mites. Instead you're probably dealing with a chronic ear infection or an allergy. You should get him checked out by a vet because using mineral or vegetable oil in his ears when that's the problem will only make it worse.
Since I assume you're using one of the above oils, don't worry about it. The worst it will do is make his stool a little soft. People use mineral and olive oil to help with hairballs if they don't have anything else around the house (never vegetable oil, though, because it has icky oils in it). You can use a warm damp wash cloth to wipe the excess off his head.
But again, please stop trying to self treat this at home and make sure he doesn't have an ear infection.
