Just to answer a couple of questions

Cloud flying is permitted in Regional and National competitions in the UK
as I type. This may change.
The most common scenario for getting caught above cloud is when wave
flying. I set a waypoint on the GPS away from the high ground, deploy full
airbrake and trim to 55kts. From then on you can sit back and enjoy the
ride. I know this works in wave conditions where the air is smooth. I have
used it to descend in clear air, never had to use it for real. Everytime I
have tried it the glider has started to gently spiral but remains stable
as long as you keep your hands and feet clear of the controls. There is
little turbulence to disturb the glider until you are below the wave,
normally this means you are clear of cloud as well.
The glider I used was an ASW17 with the double paddle airbrake mod. Flaps
at +1 or zero