You must have a very big mouth or a very small fist. It sounds impossible to do. The mouth is an opening to the body, so I would fathom you do similar acts with other orifices. Get some hand puddy, they sell it in the fitness sections of sports stores. The putty is used to build hand muscles but for you, I think will help to preoccupy your hands and help keep them away from your mouth. The puddy comes in I think 5 grades, get the easiest one, with least resistance.
Advertise that on MySpace.com
You'll make some guy a good wife. (I know men, they're all like carpets: Lay them right the first time, and you can walk all over them for years.)
Tobra - Buzzed