To me, the spare tire was more important than the Brembo's, and fix-a-flat is an inelegant solution.

Now, however, thanks to orange3.9stang, I'm having a Doh! moment. I'll be sure to mention it to my spouse, whose 2010 Camaro came with compressor and slime.

 

I think the best solution to the front VS back solution is to accept that both are bad and that you should take it easy and drive it and get the real tire fixed promptly. Besides, you don't want to be playing musical wheels with your puny tire changer jack, I'm not even sure you'll be able to get two wheels off the ground with it. Also turn off the traction control, because the manual tells you to when you put the spare on.

Ford put 20" rims on Mustangs?

 

They did (on the rear) on the 2011 GT500 with the SVT Performance Package.