Replacing internal cables
Having cut the nipple off the old cable and removed all the outer casing, I threaded the new inner into the brake lever and first section of casing, then joined the new and old cables with a length of this shrink sleeve. When shrunk it just passed through the holes in the frame, allowing the new cable to be drawn through by the old.
This, of course, only works if you have the old cable still inside the frame.
This was first published in the October / November 2012 edition of Cycle magazine.