I haven't had a look at my big if this could work:
In the eighties, a friend of mine decided the twin-cables and high-tension return-springs of the carbs of his big Guzzi being to hard to operate. So he mounted a rod on a small roller-bearing under the backbone of the frame in the middle of the two carbs. Then he put three discs with grooves to fix the cable-nipples and to run the cables in them on this rod. The disc in the middle was used for the cable coming down from the throttle. The two outer ones were set above the carbs and operated these via short cables. Thus enabled him to leave a lot of friction of the cables behind and throttle-/carb-operation (and tuning!) was much easier this way. Perhaps you can use parts of this idea for your set-up. This solution was also used on the Guzzis that were run in BotT-Races (Battle of the Twins) back in those days. Maybe, somebody here has got pics of one of those.
Kind regards, Bambi
'Find me kindness, find me beauty, find me truth ...'
(Dreamtheater, Learning to live)