I believe that the OEM accessory 18" wheels (meaning either the g-spiders or the ISP mode wheels) clear the F-sport BBK's.
Unsure if they fit in the spare tire compartment though. Best way to check would be to see if one of your front wheels fits in the spare tire compartment. If so, you're good. The 18" package has the same outside diameter/width as F-sport 19's for front/rear respectively.
If they do fit, you can buy a single wheel at the dealer. They're about $200....or you may be able to find one used. Then just find a tire, doesn't have to be a great tire if you're looking as spare tire use only.