If you cannot find a supportive voice, how about a voice angry at the negative voice? Do you like being called names and belittled? No? Then get angry at that voice and tell it to. . . [insert really long, funny, place for it to go] -- kind of like the Riddikulus spell in Harry Potter?
When you put yourself down, look at the wording and how you do it; it is rarely very complicated or difficult to poke holes in? Point out its flaws, make fun of it not having more fifty cent words :-) Revile it with all the imagination and intelligence you have and it will slink away under the onslaught.