@lbgoforth First, It requires an evaluation from a physical therapist, prosthetist/orthotist or other person with specialized training consult your ortho or primay doc for a referral. Second is selecting an appropriate shoe for building up - must be sturdy & well-fitted. Next, if you buy it at a specialty shoe shop, they may do the build up or will refer you to someone in your area to do it. Finally, you must gradually wear it, and adjustment may be needed to make it work for you - remember, your body has been compensating for that shorter leg for some time, and will need to adapt to the change. It is not quite as simple as just going to a shoe repair shop and saying "build up my shoe."
Sue