I spend a lot of time playing on 99cm Fischers. which I race on ocassionally. While these are a lot more stable than the 90cm versions, they are still not great when on their bases. Best thing is to keep them on edge, and go edge to edge, always turning, never straight down (a bit like basic snowboarding)
The other thing I found useful was to rest my hands/arms on my knees. I found that this made it less painful for me, because my lower leg was supporting more of my body weight directly, rather than passing every vibration through to be absorbed by my thighs.
Technically and medically this could be completely wrong, but it worked for me.
Oh, and don't take yourself seriously on them!
Know Powder, Know Fun
No Powder, No Fun