There's no KVM at the servers, so that's not really an option.
I was thinking of something more along the lines of somehow upgrading a bunch of files/RPMs and then rebooting into RHEL5.
In doing some googling, I found a posting
that would allow a Red Hat upgrade from 7.3 to 8.0 by manually upgrading the redhat-release RPM and then letting up2date do the work. I wonder if something like this is still viable.