Setup a queue with nothing but virtual extensions that go straight to a voicemail.
Is there anyway I could set it up so that it would round robin the voicemails instead of going to my failover destination??
This would take a custom script or a module in FreePBX. I would suggest opening a feature request but something unique like this wont happen anytime soon since 2.10 just came out and features wont be added tell 2.11 which is a good 9-12 months out before a Beta even comes out.
You could always find someone to build it for you or contact FreePBX Support to get a price to build this.