For those that are interested, I managed to cobble the Ruby 1.8.6 and 1.9.1 spec files together to form a Ruby 1.8.7 rpm (srpm here) built against Fedora 11 (yes I really need to update to F13, just haven't had the cycles yet). It's not 100% perfect, I tried to simplify the package as much as possible, removing any unneeded cruft, but in the process may have remove a couple things we wanted to keep (namely pulling the upstream ruby-tk branch for the ruby-tcltk package). But what is there is working as evident by the attached screenshot, and anything missing can easily be readded by using the 1.8.6 specfile as a reference.
Next I'm going to be working towards Rails 3.0.0 rpms and a Ruby 1.8.7 / Fedora appliance that pulls all of this in. After this we should have a base platform to try some widespread integration testing for multiple versions of Ruby on Fedora.