Thank you. I'd be happy to try to help you. I ran both the rear brake cable and the shifter wires through the fork. In my build, I used Ultegra shifter modules, which I mounted in the frame near the BB. As such, I ran six wires through the frame and fork. The key here is that you must drill two holes in the fork. One is in the rear of the fork and the other is just below, or even an extension of the existing front hole for the metal post that is used for the stem preload screw. For the hole at the rear of the fork, there is a white sticker/label which is where the hole should be drilled. You'll need to be careful in drilling these out, but the steerer tube is a much thicker steerer tube, so these holes can be made.If you send me your email, I can send you some photos taken by another slowtwitch member showing these hole drillings.

As others on this thread have described, I used a hobby knife to cut slits in the cable guides to run the rear brake cable and to run the Di2 cable to the rear derailleur.