Okay, I know I'm a bit late to the thread; sorry.

But, I do have a theory....
Mark says that you can't use any UT content. Maybe he'd allow it if you force them to have UT installed to install it (which can be done when building the UMOD), and (although myLevel fans will throw a fit) make them supply the textures and sounds themselves. so that all you're supplying is maps, music, and maybe models that they can't use without having UT installed anyways?
(Heck, I think you could make it so that paths pointing to their UT texture and sound directories--or at least the default ones--are added to the INI, so they don't even have to copy stuff over....)