What Eric meant was, if you are going to run a cable, why not run a multicore cable instead of fibre. I'm sure you can find a 10core (8 + ground) multicore, it will obviously not be as thin as the fibre, but it will simplify your life.
Edit: most multicore I know of has a shield of some description, as simple as it may be, it still solves this antenna issue...
It however can go cactus, as once, one of the shields in this particular microphone cable we were using for a production went AWOL and we were picking up a local AM radio station clear as day... not good however, considering it was a roof mounted mic and all the seating had to be moved to replace it >.<"