I bought a sheepskin buttpad from 
        
http://www.alaskaleather.com/ a year or so ago and I've used it on a few bikes. It has an elastic strap to go under your seat with quick release clips to remove from the bike. I use it as a pillow when camping. 
         
         
        
 
         
         A friend uses a whole sheepskin on his 800GS and it's nice to have as an extra bit of warmth for sleeping.