Well I'm giving it a shot. I went to petsmart and looked and the hampster balls, the 7" was too small, then it jumps up to 13" which is waaaay too big.
I decided to get one of the medium critter travel cages. It's 11" x 7" x 6"
It has all the slits in the top but I drilled some holes in the sides too for added circulation (be careful when drilling plastic, almost destroyed the whole thing on the first hole!)
It floats ok, but I used an extra medium mag float I had to hold it in place.
I put a piece of PVC and a rock with some nori rubberbanded to it, and acclimated my new Yellow Tang.
My Purple Tang and Sailfin Tang went for him immediately, and normally would have gave him a nice run, but they can't hurt him, and he's not stressing. Food goes through the holes fine to he can eat along with everyone else fine too. So so far so good!
I'll wait for me to not see anymore aggression towards him, then let him loose. I'm guessing a few days.