I did not know that you could use the shifter as a junction box. Thanks for that tidbit. Classic RTFM failure on my part. I knew there was a second plug but I thought it was just for satellite/remote shifters. I didn't come across an example of wiring that did show that as a possibility. I wish I had known that earlier since I probably could have used the wires I had on hand that way.
I actually managed to rework it with the y-cable and a longer extension cable with the wireless unit. Now it's just a possibility that the wireless unit may not come out of the handle bar as it's wedged a bit in the drop/curve. For clarification, From right to left: I have the Junction A, wire 1 runs through the bar/stem and out to the derailleurs/battery. The wire 2 (y cable) runs to the WU111 wireless unit, then to both shifters.
As CX alluded to, as with most things, the more you do it, the easier it becomes. It definitely was easier this last time as I've gotten used to manipulating the lines and wires internally and externally and using the cable puller tool. Still, it's slow, fiddly, and not "easy".
Major respect for you guys that do this every day.