If you have the standard 20" Slipstreams, you can always buy two front take-offs online and run those on the rear. I'm sure this has been covered, but running the identical 20x9 w/ 265/45r20 tires in all 4 positions allows you to rotate tires to your hearts content.
On a related note, I always carry a spare front take-off when I travel with the MX, since the fronts fit any position. When in town, the spare is in the garage and just a phone call away. I keep a 2 ton floor jack, breaker bar, and torque wrench w/ 13/16 socket in an 18 inch tool bag in the MX trunk at all times. The bag also has a first aid kit, tarp, rain parka, 12v air pump, flashlights, and a few tools. This setup allows me to change a flat or broken wheel in 15 minutes and continue on with life.