Sprinkle an emetic (a vomit-inducing drug) into foods that you want to stop eating, such as chocolate. It is well-known that nausea causes a long-lasting aversion to the food preceding it. (For instance, this is a problem for chemotherapy patients - the drug therapy causes nausea, which they then associate with food.)

I haven't tried any of this, but I'd be very surprised if this wasn't an easy, long-term solution to the problem of people wanting to eat food that they don't want to want to eat.

Maybe this could even be extended to non-food addictions, such as video games or mindless internet browsing. One person I know quit smoking cold turkey this way (by throwing up after smoking a cigarette, not with an emetic).