I have CDO1 but have not had occasion to replace the front der. housing. I believe (someone correct me if I'm wrong) that the housing runs from the shift lever through the frame to the inside of the small exit hole below the mechanism. Only the cable exits the small hole.
One good tip for any kind of interior cable or housing run is to NEVER remove both the cable and housing at the same time -always leave one or the other as a guide through the crooks and crannies of the interior of the tubing. A neat trick is to release and back the cable out a bit at the lever and cut the head button off the cable (cut right behind the button). That allows you to remove the old housing (from whichever end is convenient) and leaves you the cable as a pre-threaded guide line for the new housing. To replace both cable and housing, snip the button,reattach the cable to the mech (to keep it from being dragged inside the frame) and remove the housing. Thread the new housing over the old headless cable. Then release and replace the old cable with the new.
Two of the most miserable days of my life were in the early days of carbon frames when I pulled out a der. cable, assuming that of course there was some kind of tubing or channel to guide the replacement. Not only was there none, but in laying up the frame they had used bubble wrap to fill the empty spaces. Visualize a capped up 3" x 3' PVC pipe stuffed with bubble wrap and you're trying to push a piece of flexible wire through a pin hole at one end to exit a pin hole at the other. If you're real bad and go to Hell that's one of the jobs the Devil has waiting for you.