There are references scattered throughout the festvox documentation to a GUI program for recording speech prompts, called "pointyclicky". Sounds nice, right?
Well, if you try to find the sources, you find that it was last updated in 2000 (!), and it's in disrepair. (http://festvox.org/pointyclicky/)
It won't compile any more, but Kev 'Kyrian' Green at the redhat bugzilla patched it up so it's closer to compiling. I also made some more changes so it would work for me on Debian, but I don't remember exactly what I did. Anyway, you can download my patched version of the sources from here, which should be up at least for the next four years.