I would like to know where to get a sheepskin as several people have commented on how much they improve the comfort level - but NOT one that slides around.
I have the gel seat and to answer your question here is what I do - I carry a bar towel (small towel) and a bungee in one of my panniers - whenever I stop and leave the bike in the sun I cover my portion of the seat (including down the sides) with the towel and retain it using the bungee.... It works great and the seat is cool when I get back on.
I learned to do this the hard way - even after reading Dave M's warning, I went out to lunch (I am in Arizona, it is 110 days at the moment) and left the bike in the sunshine - it seriously burned my arse and was red hot ALL the way home - and I am not a fan of riding the Sprint standing up...
Now, based upon the thickness of my towel, I would have to assume that a sheepskin would work at least as well at stopping the seat from turning into a flaming arsebroiler as mine did!