Just to clarify, I don't think Jackson's inquiry was for an XJ. If understand correctly, he is researching the possibility of retrofitting an XJ tire carrier to his GMC Canyon. I didn't realize that at first.
Keep the suggestions coming. I too might be interested in something of the sort for my 01 XJ - preferably one that makes use of the factory end caps, with provisions for Hi-Lift and gerry can(s) ... and one with a spring-loaded latching mechanism.
Frankly, I could really use such an assembly, but having that kind of weight hanging off the back would almost certainly warrant a spring upgrade - which I'm not that eager to do. Therefore I have mixed feelings about installing a tire carrier.