Cap Registrations for Events

There are many events in which having an unlimited amount of attendees could be a huge logistical problem. I'd love a way to cap the amount of attendees and automatically switch the landing page to a closed registration when registrations have hit its cap. Basically - "If list count = X, then show X landing page"

This was also discussed in this thead:
http://community.marketo.com/MarketoDiscussionDetail?id=90650000000PFSGAA4