I think I would opt for a same size tire of any brand, hang it on the back and take it out of rotation. Maybe hunt FBM, Craigslist, Used tire stores or whatever and see what you might find.
Or just mount a 40 series tire on the wheel, hang it on the back, call it a day. I know there's a picture of a Jeep out there somewhere with that setup, but I can't find it.
Edit: Found it, or at least a thumbnail.
