taylorRichie 
You could try airing down (zero psi, or less, if you can figure out a way to create a vacuum to less than zero) a spare 33" to compress it enough to fit in the rack, then air it up as needed.
A 285/75 on a 16" rim might give enough "crumple zone" on the taller sidewall to make this work.
Also, if you have two different diameter tires on the rear axle, you will be creating undue wear on the LSD clutches.
