From what I learned when I was fiddling about with it before, I don't think it can be done. Something to do with altering the data spectators see or something. If you could let me at the internals of UTV on the other hand... in other words i don't think you can do it unless they build special support into UTV.
Is there anywhere we can post for UTV and find out what's going on? Maybe if more than a couple of people show interest they would work a little faster...
try posting on the atari forums for UT2004, though i highly doubt UTV will ever be in the game properly.....with uengine3 in the works, this probably got pushed out to that if at all.