Probably an obvious answer to this question but....how do you guide brake cables/casing through top tubes that have holes for internal cabling?
With difficulty. What I've done is get a bit of thin wire, poke a loop of it through the rearmost hole, thread the inner cable through until you think it's caught in the wire, then pull the wire loop out and hopefully pull the inner out with it. Then push the outer cable onto the inner.
If you've got an old cable in the frame already then you can just use that to run a replacement down i.e. remove old inner, push through new inner, remove old outer, thread on new outer. So you only really have to do it once.
With difficulty. What I've done is get a bit of thin wire, poke a loop of it through the rearmost hole, thread the inner cable through until you think it's caught in the wire, then pull the wire loop out and hopefully pull the inner out with it. Then push the outer cable onto the inner.
If you've got an old cable in the frame already then you can just use that to run a replacement down i.e. remove old inner, push through new inner, remove old outer, thread on new outer. So you only really have to do it once.