I've used single or double gang boxes with the top and bottom cut out, wires labeled right at the box, and let the extra wire just drop down into the wall void. As long as there aren't way to many, it's pretty easy to get to that one wire you need.
I've also done this on a pre-wire to protect the wiring from the drywall butchers.
Have also done the same with a distribution enclosure.
Last edited by Trunk-Slammer -Supreme on May 19, 2018 18:37.