Hmm....
The skies would have to be a vehicle - that's the only way I can think of to be able to get in/get out of them.
I've seen a field gun that was towed behind a truck, but the gun obviously didn't have an engine...dunno if you can tow a vehicle capable of moving on its own.
The last problem is obviously how to make it impossible to ski uphill - if you wanted to go cross-country, you'd need to give the ski vehicle a silent engine...things have a tendancy to roll downhill so perhaps you could limit the top speed of the skis - that way they didn't have the power to get up hills but could traverse flat ground at a modest pace.
I'm not an addon maker...but it seems possible