I've only been able to find one doc on CCO that demonstrates how to move FWSM traffic out to an external IPS appliance and then back into the chassis for forwarding to the rest of the network. It uses "auxiliary" VLANs.
FWSM routing and switching for my inquiry are all occurring through blades in the 6500 chassis with only the IPS being used located outside the box.
...it has a little section toward the bottom in the trouble-shooting section that mentions their one aux VLAN solution.
Anybody got a better more complete reference for this scenario?