Changing garage light socket to outlet, found wiring problem
As far as the GFCI code doesn't specify the location. There used to be an exception for outlets over 6.5' but I think that is gone now. I would add a new wire so you don't have the safety concern. If the walls are closed you may have to fish the wires through the walls because the old wires should be stapled to the studs and pulling the new wire with the old won't work with the staples holding them in place.