The other method, which seemed much cleaner, was to use "0.7.3" for rh73 "0.9" for rh9, and "1" for fc1.
That method was proposed about 3 time VERY LOUD on the -devel list (with using fdr or whatever distid), but no RH people commented, so it was dropped or better died after a silent death in an agony of 4 or 6 weeks.
This has all been presented on -devel, please check the archives.