I am coming at this from both a standpoint of a full size power and glider pilot and an RC glider enthusiast.
I certainly understand the the concern of all parties including the RC glider pilots.
AMA sanctioned contests could gain exceptions to this rule by contacting the FAA regional office and perhaps gaining a few day TFR airspace area. This is done for the model rocket enthusiasts as I have been warned of these airspace restrictions when I fly my full size airplane near dry lake beds next to Edwards Airforce base.
All this his takes a little more work, but it keeps everyone in the loop.
It then becomes the responsibility of the full size pilot to gain all information about their flight and anything that my affect it. At that point the RC pilot and AMA would not be liable.
It it will be more difficult for CC RC soaring contest because of the larger area of flight, especially straight out flights.