This may sound corny, but have you considered a pair of electric socks?

Hear me out. If your kilt is heavy wool (perhaps with some polyprop. shorts beneath for extra warmth) and your feet are plenty warm, I doubt, even in the powder and cold, that your knees will not receive alot of benefit.

Also, one other recommendation. Warm up your knee joints ahead of time with a heating pad for about 15 mins. That should keep you flexible and free!

In a worst case scenario, put on a pair of polyprop. long johns and go for it!

And for goodness sake, get a good pic or two!