In the early 70s, there was an aftermarket company that made just that. My dad had one installed on his new 73 Dodge truck. On the bedside behind the rear wheel on the passenger side was a rubber surround with a "key" slot that released and lowered the spare on a cable that could the be dragged clear of the truck and removed from the cable. It also had a nut that you cranked with tire tool or 4 way to raise it back up. Seems like it was literally called "Spare tire caddy".
