I'm not sure that the spare tire mount will support the weight of the larger tire, but I could be wrong.
Also, I'd think that you wouldn't be able to see much out the rear window, with the larger tire?
Guess you could always use the roof rack...
Update: Check out the picture in the reply for this thread:
Wheel and tire combinations
Apparently, the tires are close to your prospective ones, and it could be that the mount on the tailgate is stock...