I did a rewire job once over a crawl space. We drilled a very small hole through the floor an inch from the wall, poked a wire down and then the helper in the crawl, measured over 3" from the wire and drilled up into the stud cavity. We established a standard of N/S/E/W to be sure we were going the right way. Something along those lines might work, using a plastic box that you can drill through.
