I spent several years doing just that. We would go out and ski with clients and video them doing a variety of exercises designed to illuminate stance and balance issues. We then went indoors, did measurements and made modifications based on the measurements, and went back out and repeated the exercises with video and then went back in to watch it all on tv.
The results were quite remarkable. It was also difficult to charge enough to make it worthwhile from a business perspective.
On snow analysis is great at telling you if something is wrong, but not what is wrong. That is best determined indoors.
Orthotic fabrication, cuff alignment, and canting can be most reliably determined indoors. Sometimes, fore/aft balance benefits from further on snow examination.
I still go out and ski with people a few times a year, we charge $100 an hour for this, but it is almost always a movement issue not an alignment issue that is causing the problems. And although that may sound like a lot of money, it is a loss on our end.
We do work closely with most of the top Ski Pros here and they can act as our eyes on the hill with their clients and are better suited to offering movement alternatives than I am.
Finding a good bootfitter who works in conjunction with coaches or instructors in your area is your best bet.