Printing orthotic shoe lifts?

My son (8) has a condition which causes overgrowth on half his body. His left leg is currently ~4cm longer and our orthopedic dr wants him using lifts until surgery in two years. Custom lifts are pretty pricey especially since they need to be installed on the outside of every pair of shoes he owns.
Has anyone printed external lifts? I imagined scanning the contour of the sole then basically extending that down a few cm, adding some style for points :).
Also interested in material suggestions.