Is it outside the realms of possibility to put your game server on a new IP and behind a VPN, email all your clan/server buddies who play on it with the VPN details and strict instructions not to share it out?
Then as you guys have packed up and moved to a different area of the net and you are no longer advertising your IP, hopefully he will move on to another target. After a few months consider setting up in public with a new host that has better DDOS protection.
I'm sure there might be a gaping hole in my plan, but I've had a few beers so please excuse me if there is.
Good Luck