When I received my new Instinct 999 MSL frame it included some inner cable liners run through the frame to use as guides for the shift, shock remote cables and seatpost remote hose routing.

The shock remote had a cable liner pulled in the frame. An important note on the Instinct MSL frame (and likely the other carbon frames as well), the shock remote is intended to have a full length cable housing, there are no cable stops in the frame (which I discovered just after trimming the supplied cable housing to length assuming there was a cable stop in the frame). So you run the shock remote inner cable through the cable housing sized for the entire run, and then through the guide inner sleeve, and then use the inner cable to drag the cable housing through the frame and pull the liner out.

The shifter cable internal routing has cable stops at the headtube entry. If you were going to use standard cabling systems for the shifter cables, then you could use the same approach, run the inner cable through the handlebar to headtube cable casing and then run the inner cable through the liner in the frame until it comes out through the cable stop plug at the BB. Once it has made it that far, you can pull the inner sleeve out and install the cable access plug into the frame and install the derailleur cable loops at the BB. Definitely a good idea to apply some synth grease on the o-ring that runs around the cable stop plug, makes it easier to extract later.

If you install the cable stop plug and then find you need it out again, a used spoke J bend makes a handy tool for that purpose, using the gap around the seat post remote hose/cable.

If you were going to install Gore Ride-On fully sealed shifter cables, you're going to need to remove the inner cable guide sleeve as part of the fitting process, since you really need to get the cable casing cut to size and then install the inner cable liner and get it cut to size before installing the inner cables.

The easiest way I found to get the Gore shifter cables down to the cable stop plug at the BB begins with removing that cable plug. Then take a 4'+ long piece of old shifter cable inside a 3' long piece of the inner liner, with about 18" of inner cable exposed at the BB end. If you feed that into the cable stop in the frame at the top and use gravity to to get it pointed toward the hole for the cable plug. The inner cable keeps the inner liner straighter and will find the hole in the bottom bracket more easily. Once the cable and inner sleeve appears at the BB hole and you pull the inner liner down to the point where you have about 6" left at the top, you can pull the piece of inner guide cable out and insert that piece of inner cable at the top and into the the new Gore inner liner at the top and run it into guide sleeve and Gore inner sleeve. Once that new cable is more than half way down the inner guide sleeve, you can push the new Gore inner liner in from the top until it pops out at the plug. Once they are both run through the plug, the plug can be inserted in the frame.

Once the Gore cable casing and the Gore continuous inner liner are both cut to size and in place on the frame, the Gore inner shift cable slides through quite easily. Sometimes it will be a bit reluctant at the loop for the front derailleur.