In reply to pej09: Apart from only 8 hours of daylight (if the sun is shining), the logistics could well spoil the trip. You won't be allowed to camp in the ski areas, the lift closure sweep teams will move you down and won't discuss it. Anywhere in the valleys is private property and a tent will attract attention; to avoid this you'd have to carry a lot of gear, food, fuel at high altitudes using either skins or snowshoes, and that's more tiring than you think. Lets assume you get to eat, boil water (from snow) and sleep, next morning, boil water!!,you then have to leave your tent in a exposed place and walk back to your car in what will be an odd place that will attract attention from the Police or thieves with a lot of valuable kit inside.
Ski all day, good, and then return to try and find tent in pitch black dark assuming the weather is good and it hasn't snowed all day and buried your tent to the point where you can't find it. This sounds like a ridiculous exaggeration but I've been in car parks and people can't find their car in daylight after a heavy snowfall and they can see the footpaths!! Find tent, boil water etc...and see article re CO poisoning in a tent.
http://www.headbaby.com/water-1.htm
Sleeping in a car doesn't attract attention but the other posters have pointed out the drawbacks there, but bear in mind everything you do before and after ski-ing will be in the dark and it will be very very cold.
If you do succeed, you've got to write an article on the experience. Good luck