Many people use braided cable, thin solid wire, and solid .093 rod for controlling rudders and elevators without ever having issues with radio interference.

I still fly 72 mhz and run a wire antenna from the receiver.
I run it outside the fuselage and back to the tail.

Two of my favorite materials to make pull-pulls with are thin brass wire (.030) and the thinner gearshift cables from bicycles. Both solder easily. I've also used braided cable used on the back of heavier picture frames.

I've heard this story about radio interference from pushrods and cables but never seen evidence of it. Having said that, I never allow one metal pushrod touch another, or allow pull-pull systems crossing to rub off each other.