They don't have a stand-alone display on the bike. Generic controller that 'could' be hooked up to SW900 but that would still be useless in his situation. It really depends on if he wants to spend $100 USD to fix the problem electronically or go through all the wiring combinations. If yes for $$$, he can get a KT LCD3 display and KT 26-30A max controller and fix the problem after getting a compatible PAS sensor as well:
Parameter C1 allows both forward and reverse phase waves (sine or square; they are shown as square in the diagram).
KT LCD3 Manual --- C1 is Page 24/25
If he uses a standard PAS sensor on the left (non-drive) side, he can make the motor's wave reverse by pretending the PAS is on the other side and choose 5, 6, or 7 in C1 for the reverse waveform. That should take an already reverse waveform and flip it back to forward. The reason I know this is because it happened to me a few years ago with a different hub motor. I could not get any power, and then finally played around with the C1 settings; wheel direction started up and reversed in 0, 1, or 2 and went forward in 5, 6, or 7. Normally the wheel goes forward in 0-2. Set it to 5 and it was fine after that.
Did not have to bother with rewiring anything.
But in his case he has to decide if he's going to throw money at the problem or not.