Revoke Supporter Features upon Cancellation of Subscription.

We have premium themes setup in our instance of WPMU and Supporter. When a supporter cancels his subscription he still has access to the premium theme. Is there a way that we can remove all supporter priviliges if someone cancels their account - basically default them back to the regular template and deactivate anything they were using. It seems like it's a pretty simple way to game our system by just purchasing 1 month and then canceling.