60B: Routing Between Interfaces in Interface-Mode

I have a 60B with three WAN connections and it is in "interface mode".  All six interfaces are independent networks with their own IPs, DHCPs, etc.  It is all load balanced and working correctly.  I would like to route traffic between two interfaces or even possibly three.  I've tried many methods without much luck.  Can someone post a solution for me?  Thanks to anyone who replies.