2 inside NAT interfaces with 2 outside interfaces

I have 2 internet connections coming into my router, one is the primary connection and the other is a failover connection. Currently I have my primary connection plugged into to ge0/1 and my ip nat inside source list interface is ge0/1. When the primary connection goes down the failover automatically routes traffic across my vpn but internet traffic is lost. Is there a way to set 2 inside nat source lists or a way to configure some kind of dynamic nat? Thanks.