I now know the punchline to this joke so in case somebody else is suffering, here it is:
A bus fault triggers an exception (interrupt) handler. A bus fault can happen when a non-existant memory location is read or written.
A double bus fault happens when an EXCEPTION HANDLER causes a bus fault. In other words, your exception handler needs an exception handler, and Coldfire doesn't do that.
So for the most part, my solution for Double Bus Faults has been to issue a "halt" command in my exception routine (only when DEBUG mode is enabled), so I can crawl up in there with my ICE and find out what happened. When DEBUG is disabled, the default is (usually) to do a hard reboot, which continues to work.