My daughter has a Nishiki NFS B with internal cable routing and my new(to me) Olmo has internal cable routing. Both have tubes that connect each end. In each case I was surprised because the LBS guy told me never to buy a bike with internal cable routing because they dang near impossible to feed out the other end. He was running a Trek shop.

I have heard back before Trek bought Klein that they had a plastic tube inside than ran end to end.

If you have a good magnet, you can let a cable end sit for a few minutes on the magnet. Feed your cable from one end to the other, then take the magnetized cable and feed it into the end that you want you cable to come through. If you can get the ends to touch and have a feather touch, you can push/pull the cable through.