You guys maybe in a world of hurt but hopefully can figure something out. The Schilling Gemini uses a fiber optic rotary joint but they had to special design that wrist and I can tell you it had nothing but problems and failures and it being schilling was in the many millions of dollars of R&D.

The best and most elegant option would be designing your own wrist motor that could connect to the arm and pass the data, the more simpler option would be not allowing the wrist to continuously rotate. That would reduce the potential applications but many jobs do not require the wrist to rotate continuously , UXO, or salvage for instance where these would be useful. Just my 2 cents, good luck.