How to make HA Heartbeat failover when either of two NICs connection is lost?

I was successful in configuring a simple Heartbeat setup on Ubuntu 12.04, which will fail-over two VIPs to a second server when BOTH Ethernet links fail. What I can't figure out is how to fail-over two VIPs when either of the two NICs loses a link connection. Heartbeat will detect the link is down, but until both go down, resources will not fail-over. I'm not using any cluster management like Pacemaker. I would appreciate a point in the right direction.