I wonder about the possibility of coordinating this behind the backs of hostile regulators. If you make the deals anonymously, you need a way of verifying that the other party follows through. Maybe you arrange the deal on an anonymous clearinghouse, use encrypted communication to agree on an irregular amount, both escrow (at least) that amount, show each other the receipts (you don't need to conceal your identities from each other, just from observers) with the odd amount serving as verification that it's your transaction, then release the escrowed funds?

No doubt there are less amateurish crypto-transaction designers than I reading this who can weigh in.