I started this post to help you with running a cable through the frame. On some bikes they make a larger oblong hole for the cable. Then a molded plastic guide fills the gap.
In these spoiler photos you can see the angled plastic inserts. To fish the cable through use a snake. At work I use a snake to fish wires and cables a lot. Push the snake up from the bottom hole, when you see it at the top, hook it and pull the snake out the top hole. Now with one insert slid up the cable, tape the snake to the cable and pull it back down through the frame.
I also make the snake, I use thin mechanic's wire. Cut a piece twice as long as you need it. From the middle of the wire, bend it back, (two ends next to each other). Put the loop end in a bench vise, grab the two loose ends with vise grips, and start twisting. Keep twisting, also push up on the belly of the wire, and relax it while you are twisting. This will move the twist all the way up to the vise. Stop twisting before the wire breaks or double knots. Don't release the vise grips. Use side cutters and cut the new snake off the vise grips. It un-spins just a turn or two and the cut ends stay together.
