Technically, I think that since you were an intermediary, you could say that this was a loan and litigate for repayment of the loan. However, when the judge asks what the loan is for, you will be admitting to a crime and also implicating your bookie in a crime, so it's not a very good idea. Besides, all the judge can do is issue a judgement - it would still be left uncollected until you get the money, this would essentially just create a public record and official ruling.
Your best bet is to have someone go collect. After all, it has to be paid, it's his debt, and if you don't have that kind of money to cover it then he will have to be the one to caugh it up. Unfortunately, the only people I know for that keep 50%, which would only get you $2000, and I'm not certain that they would travel much for that much money, so that may not be an option for you either.
If nothing else, as was suggested before, make sure every book maker you can is aware of who this guy is. I'm guessing he's already blacklisted though, which is probably why he was going through you to place bets.
Jerry Garner
jerry@gamingbroadcast.com