I'm amazed that people try to use large headsets in Self-Launch Sailplanes. They are an excellent way to scratch the inside of the canopy. Also something to store when not in use, which is 95% of the time as I recall.
There are many "isolating ear bud" headphones available these days. Examples:

Shure
http://www.shure.com/americas/produc...s/se-earphones

Ultimate Ears
http://www.ultimateears.com/en-us/900s

Ear buds are available from manufacturers or on Amazon, etc. for much less than an aviation headset, and fit in the glider's side pocket.
Install an 1/8" stereo headphone jack and use the same boom mic!
Jim