I don't know if you've ridden an internal hub before, but finding the gears without the indexing built into the shifter is pretty tough. It's tough on an AW, I'm guessing it's REALLY tough on a hub with more gears. Even Sheldon said it was hard to find two with his barcon-operated AW. I can attest that on my AW-equipped mtb frame, if the cable goes out of adjustment, I'm screwed as to shifting without fixing it.

So, I suspect you can use a friction shifter, but I don't think it will be fun.