proxying on extensions?

Can one proxy off an extension?
Meaning, can I specify that all files ending in .foo should be proxied using
a class extending the ProxyFrame?
I'm going to play around with adding a .foo extension to the default indexer
then attaching a FooFileResource (extends FileResource) to it along with a
FooProxyFrame (extend ProxyFrame).

Is this crazy or a reasonable thing to do with the ProxyFrame class?
TIA,
Dan