Was working on my bike and noticed that the radiator cab is rubbing on the brake cable. It had worn through the protective cover and was starting on the cable plastic. I wrapped it in electrical tape and will just check it every so often.

 

I would cut a small piece of fuel line and slit it, then wrap it around the brake cable in the locartion where it is rubbing and tape it in place.
The tape you put on will wear through quickly. You should see if you can use a cable tie to secure it away from the radiator cap.
Good luck.