It sounds like it would be doable (and not a lot of work for Meg
) if:
1. There were one thread for keeping track each month
2. At the beginning of the month (or whenever the person wants to start posting comments), they checked their gallery stats to see the number of comment they had as of then. Then post that number in the thread.
3. When you get over the magic number, you make another post (or edit the first) saying that you've done the magic number of posts.
I agree with LeeAndra that it could be sort of an honor system, or at most someone could do occasional spot checks if people think that's necessary.