Sorry to say but you have just lost a potential player if you cant fix this problem in the best way. He is one of bitcointalk active gamblers who can wager much more than most other regular bitcointalk members. It does not make senses for me if you accuse him as bonus abusers, I cant believe it it obviously unless you can show us valid evidence for this accusation against him. His withdrawal amount is just small amount of money and I dont think he will be risking his own bitcointalk account to abuse your bonuses.