Apparently some conspicuity trials were run on gliders a few years ago, the best results were obtained by applying silver mirror finish vinyl on the moving surfaces. Obviously nothing will help in a head on scenario but I understand it worked well otherwise. Why it hasn't caught on is another question.
To be fair, I think Il Duce's original point was more to do with the percieved wisdom of gliding in those locations, combined with radio silence, rather than the general rolling debate on use of radio / transponders etc etc.
I accept the best thermals are always in Class A!!