This idea may not be applicable in your case, but just in case...

A friend was replacing the rear derailleur cable in his bicycle, which ran through the chain stay. Once the old cable was removed, there was no way to thread the new cable. It wouldn't find the hole to exit the chain stay. So, he took a spool of thread, fed a couple feet into the "input" hole of the chain stay, then used a vacuum cleaner to suck the end of the thread out of the exit hole. After that it was easy, connect the thread to a string, connect the string to the cable, and pull the cable through.

Is it possible this technique could work for you?

tanstaafl.