I wouldn't recommend traveling very far or fast with a space-saver spare since the two rear tires are slightly different sizes - puts some wear on the limited-slip differential. I would just drive to the nearest tire store.
With one stock tire and the other replaced with a space-saver spare, the two tires will have different diameters.
Heres what I have done- I use the stock rim and have mounted a 235/50/zr18 as my spare- it clears everything and fits the front and rear- It does not fit the stock recessed hole in the car but I let it ride on the top with a cover and have it attached with the system used on the mini tire in the non gt 500 cars- It is the right height and is ok for a short emergency drive to a safe spot or to get to a stop off point to get the car on a proper tow rig. It does fit and I have now two options- a spair and the inflatable fix if it is a minor flat. Peace of mind I guess.
Can you post a picture of your trunk with the spare in it? I just can't visualize how you have the tire secured with the factory hardware when it is not in the well.
I will try to post a picture- the parts I used are in post 18 which would hold the mini tire in a gt as I do not own a gt I would guess that is what it is there for- My tire sits on top of the carpet with a toneau(sp.) to hide the tire and the pull down clamp and to make it look finished- it pretty much fills the trunk- I also have to carry the scissors jack and lug bolt wrench. I drove with it not attached until I found the parts in post 18. If you look you can see which would work- not handy with the camera and sending pictures but will try. I had to extend the bolt with the hook to adapt it to my tire- It has an offset because it does not center on the perfect spot but works.
