A suggestion I have seen to control use of credit cards in gambling online is to make the collection of such debts unenforceable in law. This suggestion leaves offshore casinos liable for winnings but unable to collect losses and effectively ends such gambling by making the property rights in an exchange of gambling services insecure.
This interesting proposal seems to have disappeared though I recall it being discussed in the Australian press. What happened to it? Maybe buried in here somewhere?
Another suggestion is to allow clients to sue credit card companies for debts accrued when credit cards are used for online gambling. This latter suggestion is well-known (see here) and has already been played out in US courts.
Some credit card companies such as Visa Hong Kong and the payment service Paypal have already prevented clients from making transactions to fund online gambling.