For testing purposes I like to be able to use a different configuration for rhgb. In my particular situation, i want to use the xorg nvidia driver ("nv") with rhgb, and later use the nvidia binary driver ("nvidia") when running gdm/X. In this way, I can write an init script that will check if the nvidia module is installed (after a kernel upgrade, for example) and compile/install it before running gdm/X.
Done, starting with rhgb-0.13.2 , if there is a /etc/rhgb/xorg.conf file it will be used to start rhgb X server. I have used it quite a lot for debugging last week, seems to work fine. rhgb-0.13.2 was pushed to rawhide today, it should show up on the devel later this week. Daniel