I've heard of this in 2 cases.
1. You have a full time, insurable career skiing like ski patrol, certain levels of ski school, disabled sports.
2. You have posture issues or another problem not caused by skiing in which you can have custom cork beds made that you can put in pretty much anything including your ski books.
I have yet to hear of someone's insurance covering custom boots because of problems caused by the wearing of boots unless they are in a skiing career.