so if i can snake the cable up somehow I should use it to slip another brake cable housing back down the fork as a guide if I have to change cables in the future. correct?

That's what I'm thinking. I've never done it myself yet as I'm actually building up my D6 right now.

It's kind of a pain in the ass, but it sounds like that's the only way we can replace cables and housing in the future. Although it sounds like, the orange cable guide will be really what you need since the brake housing won't go through the fork.

I got a wire to go thru once.. but couldnt get any further.. There is no orange guide so I tried using very small pv tubing but it didnt work. I think Im stuck with external cable on the front

Sorry to bring up an old post but in the process of trying to convert my 2011 Fuji D6 from ultegra mechanical to di2, I spent 4 hours this afternoon trying to fish the front brake cable and/or the orange guide through the front fork after switching to the TT brake/di2 shifters.

Then I found this video and did it in 2 minutes. I used dental floss attached to the brake cable with a clamped on cable end protector with the end cut off, feeding from the top of the fork and vacuumed the floss out the fork opening. It was amazingly fast and easy, and anyone rocking the external routing can probably use this trick to get back to stock internal routing...

http://velonews.competitor.com/...cable-routing_332533

Now I feel stupid that it took me so long. Hopefully if this happens to someone else, they'll find my post.