This Thanksgiving, two of my friends stayed for a visit. One's a surgeon and the other a psychiatrist. I showed them the original post. There are quite a few things that need to be ruled-out and the pain in the second leg may have nothing to do with the original injury -but it is possible and like you said, rare because it's possible the pain is coming from some other place and registering improperly in the brain. If the primary and intermediate doctors rule-out the more obvious things, he needs to be in the care of a neurologist -and of course the continuing care of family and good wishes. There are ways to isolate the nerve that's sending the pain signal and there are treatments for it starting with electrical therapies, medications and advancing to surgical procedures.
Good luck to him...