why not just carry a space saver from a regular GT with 18" wheels?
As long as it bolts on and clears the rotors then you are golden.
The issue with the bicycle tire on our Bullitts is the diff, do not put it on the back end! But, no reason at all not to put it on the front (other than the craptastic handling that would result).
So, front tire goes flat, put the spare on the front, as usual. Rear tire goes flat; change the front to the spare, and then move the good tire that came off the front on to the flat on the back. Good to go.
Sure, it's extra work if a rear goes out, but sure as heck beats waiting for roadside to pick you up and then leave you stranded at a tire shop. And heaven forbid what would ensue if you cut your rear tire somewhere you get no cell service...
Is an old trick from the Taurus SHO world where a (fairly) common upgrade is to put 13" Cobra brakes on the front end. The Taurus space saver will not clear the big brakes, so they pull a good tire from the back, put the spare on there, and then put the good tire on the front - just the reverse of what we need...