One other possible solution could be to have what Mini-Maul Evo (I think it was that one anyway) had a few years ago. It had a spinning bar quite large in diameter too (~70cm I believe) but to deal with the link problem, the robot had a small pod that extended about 30cm out the back of the robot and cleared the reach of the bar to house the link and the LED. It would be extra weight but wouldn't be as much as what would be gained by extending the full back end of the robot.

Yes it could mean that machines might try and attack that small pod in order to immobilise you, but if you make it strong and compact, and have a suitably placed spinning bar as a deterrent ( ) it should be fine as a solution

Or you could go for a hollow shaft design :P