I don't have any advice rooted in science or medicine, but as far as habit breaking goes, I had a similar situation when I tried to give up soda. I would go a couple of days without drinking any at all, then I would succumb to cravings and have maybe 3 cans of soda in a day. I think for some things you have to wean yourself off them. In my case, if I felt cravings I would have a soda, but try to limit myself to 1. Then I would set small goals for myself, like trying to go through an entire week without soda. Eventually I stopped drinking soda completely for about 4 weeks, though I do still occasionally drink some (and I've been particularly bad this past week...).
After having soda again after a couple of weeks, it really didn't taste as good. I think it was a sign that my body had curbed its sugar cravings at least a decent amount. I think a similar approach could work with your cravings of chocolate. Another possibility, which I personally don't know too much about, is perhaps a switch to dark chocolate?