B.M.
My kids all pretty much self-weaned @ 18, 22 & 15 months, the only one I had to "help" along was the 22 month old (& she was only night time at that point). What I did with her is that I just didn't offer it and tried to distract her when she asked for it.
If you are co-sleeping this might be a little more difficult for you. If you plan to continue co-sleeping, try getting a little "bed" (those fold-out foam kid's couches are GREAT) for him to sleep on next to your bed. Get him to sleep like normal and then move him into his little bed. He is still in the room, but not feeling/smelling you all night and "snacks" are not easily accessable. It may make for a rough few nights in the begining, but stick with it for a few days, it might work!
Good-luck!!
~ B.