Its not so much the USPA that has a rule prohibiting it. It's the FAA. They do not allow jumping from any aircraft (plane, balloon, ultralight, chopper) etc.. without the use of a dual container parachute system. If you want to jump a base canopy out of an aircraft just pack it into a dual container without a d-bag. Seen it done, problem solved. Also, as the jumper don't really have anything to lose (besides your life, and maybe your gonads from a snappy opening at terminal) It all comes down to the pilot getting screwed.