How about a stock 18" front wheel with a used 225-45-18 tire (instead of 225-40, thus being the 26" diameter of the rear instead of 26") installed on it?

Has anybody tried this?

This would:
1) Be approximately the same 26" diameter of the rear so you do not put too much wear on the differential.
2) Be the stock width if used in the front (it looks like the extra 1" overall diameter-1/2" at the tread at any one point-will clear the bodywork for most of the steering movement).
3) Live much longer than a temporary spare if you are many miles from home.
4) Not need any special length bolts like using a MB spare.
5) Be inflated and ready to go right when you need it beside the road.

Thoughts anyone?