After your customer decides where they want the new devices installed in existing drywalls, you can drill (or nail) a 1/8 hole at these locations into the attic (or floor), push a bare #14 CU about 3 feet long into the 1/8 hole then go into the attic or crawl space and locate where you want to drill the hole. The shinny copper wire is really visible with flashlight in dark attics or crawlspaces.
