Front wheel would work as a rear wheel in a pinch. As for a location to store it, I see three possibilities:
1) Behind the seats. If you or your passenger is short enough, you can fit the wheel in the gap between the back of a seat and the engine shelf.
2) Roof rack. You could get a Yakima roof rack and carry the wheel like an offroader would.
3) Behind the tailgate. There are various systems out there to carry spares using the car's tow bolts, though I'm not sure how many of the manufacturers are still in business. An alternative method would be to have a towing hitch installed. Then you can use any of the many hitch-based carriers on the market.