Turning Domain Mapping Off After Pro-Sites Trial

So I've got Domain Mapping set up as a Pro level option on my sites, so people are able to connect their domains during the trial. The issue is, when their trial ends, their domains continue to be mapped to the site. Is there a way to redirect those incoming domains until payment is made?

I can manually turn it off through my host, or I can go in and disconnect it through domain mapping, but I figure this should be something that should be automatic, and that re-connects it once payment has been made.

Suggestions?