maybe talk him into betting same amount of games but at lower values, tell him to record his plays for 6-12 months, find out just how good a capper he is---maybe when he realizes he sucks and that he's losing a fuckload of $$, he'll either stop, or start consistently tailing some good cappers without fluctuating.
It's his life you gotta respect his choices, you're not his mom or dad, he's a grown man and has to deal with the consequences of his actions. If it puts him in the poor house, hey as long as his head's above water and not stuck in some gutter, he's better off than alot
just my perspective