Pay 50BTC to become a VIP, and then be able to change your username there.
Or, have a good reason for theymos to take time to change it manually. I doubt this will happen though - it rarely ever does. You might need to have contributed to the forum, but don't quote me on it.
Is this really how expensive it is just to change your name on a forum. Who, in the right mind, would do this? I just don't see the point of doing it, you can just make a new account, can't you?