In order to do a seatbelt on skis you would have to take your hand, reach across the FRONT of your body, and grab the opposite tail. It would be like a stalefish/cuban but reaching in front of you instead of reaching behind. I can't say I have ever seen a seatbelt on skis. +K is someone can prove me wrong.
I don't know how you would combine a seatbelt and stalefish unless you managed to put your arm directly through your body (as opposed to in front or back).