According to the tech support of another board, the guaranteed way to remove all posts for a single poster is to delete the poster from the board.

So if birdstrike as a name is *deleted* (not just banned, actually deleted), then all your posts would go away - along with any thread you ever started, thus removing the posts from within that thread as well by everyone else.

That works on a version of php, not sure if it would work on this one.