Rotating fitting for copper/steampunk faucet?
I would try to use a push to connect fittings such as   shark bite . You could have a male threaded connection coming out of the Copper tee and a shark bite fitting  with the female threads on one side attached to that which would allow you to rotate the outlet pipe back-and-forth.

I don’t know what the long-term affects would be on the rubber o ring  inside  The fitting by having it swivel back-and-forth. It’s worth a shot as the water supply would not be constant inside the fitting because the faucet  handles will be off most of the time and if it develops leak you can replace it with another one  easily.


  EDIT: After poking around on the world wide inter-tubes i found these rotary unions i think they would work great.