This is quite a bind. From what I can see, the wireless JBL subs don't have speaker-level inputs. So even if you were willing to run your zone 2 speaker wires to the sub, then to the speakers, you can't right?
Honestly what you might have to do is buy an inexpensive amp with a sub out for the bar area, and run the Yamaha zone 2 line outs to it. Then the people in the bar will be able to control the overall bar volume from there. That would at least allow you to keep using that sub.
Otherwise, get a different sub with speaker-level inputs and do the first thing that I wrote.