The problem is that UA prepaid cards can only pay for flights of the guy the card is issued to. How could a nonexistent friend get on a plane (if he's not a Cello)?

Otherwise everybody could get a 1K prepaid card and simply pay flights of his family, friends or other FTers with it, or, if everything else fails, sell discounted flights on E-Bay.

It might indeed be possible to issue a prepaid card for a Cello (or a piece of your armored luggage). But this means that your luggage has to travel on a fully paid seat next to you. But yes, UA will issue SWUs in the name of "Weero's luggage", and those are fully transferable to Weero or anybody else. As long as the luggage doesn't object.