I ran the junction B cable (the one down by the BB) to shifter cable up through the frame and then alongside the rear brake cable to the left shifter, externally.
Then internal bar cable from left shifter to right shifter.
Finally an internal cable from right shifter to bar end junction.
I'll need new levers to do this (the R785 are single port) so I'll save it for another year when there might be better bars available anyway. But thanks for the info.
I ran the junction B cable (the one down by the BB) to shifter cable up through the frame and then alongside the rear brake cable to the left shifter, externally.
Then internal bar cable from left shifter to right shifter.
Finally an internal cable from right shifter to bar end junction.