From my understanding, the whole process of lowering your BAC goes something like this. Eliminating toxins is the liver's job. And, while it may be true that each person gets alcohol out of their blood stream at different rates, the speed is not dependent on or affected by caffeine consumption, which is rather unfortunate for those looking for a quick fix in order to drive, work, or otherwise function normally in society.
However, as long as you're not driving or being tested for your Alcohol Levels, there is some help. Coffee will stimulate your nervous system somewhat. This, in turn, can give you the illusion that you are clear-headed and awake, which is almost, but not quite as good as actually being clear-headed and awake.