I worked 2 seasons learning ski boot fitting from a great fitter. Grinding, heating and stretching ski boots. At one point we had a machine that you would take very warm hard shell ski boots, the customer would put them on. Their knees would be adjusted to the correct angle and then a inflatable boot was put over the ski boots. Those inflatable boots would mold the hard shell perfectly to your calfs, ankles and feet in the correct angles.
Edit: I stopped working with feet because I saw some nasty feet lol not that mine are pretty but yeah, some nasty feet out there......same reason I couldn't be a dentist or a few other things