The double spare tires has been done for years. My dad and a couple club guys did this back in the 70's. As I recall, they just used some stainless hex stock and threaded both ends. Then some short studs screwed into the lug nuts. The first spare was slipped onto the carrier, and the hex bars were tightened with a crescent wrench holding that wheel to the carrier. (That was my job as a kid!
) Then the 2nd spare was lifted up by my dad and I screwed in the lug nut studs. I think they look cool on the right vehicle.