The orthopaedic back inserts are the same for left and right, so if you find another drivers seat that's ortho, you can strip that and swap the lumbar inserts. So long as the leather style is the same, early cars had multiple stitching style on leather, late had wider and fewer.
All thats required then is a rubber t-piece and extra length of plastic piping to run the lumbar air pipe from drivers side throught to pass side. Assuming you already have lumbar on drivers sider.
talbir