July 2012 update. Works perfectly on my 2013 GT Premium vert. Got the DR31 18x8 35 offset rim; works the same as the DR34.
Kellen is no longer at Discount Tire Direct, but everyone there now knows the setup. Call them up and give them the parts list on this thread, and in three days or so the whole setup will show up at your place for about $280, shipping included.
You really cannot tell that the tire is there when you put the trunk mat back. It sticks up negligibly. The guys who are talking about it sticking up a few inches are talking about the full size Brembo wheel. Does not look like a kludge at all. Still looks factory.
There really is no logical reason to omit the spare on Brembo cars, other than saving one or two hundred bucks. The fantastic thing about Mustangs is that when the bean counters at Fix Or Repair Daily Motor Company cheap out on something, there's this huge base of enthusiasts on forums like this, and the aftermarket that serves them, to fill the hole.
First American car I have ever bought new, and I'm over 60. There were tiny build quality glitches (ambient lights, pool lights) out of the factory, but Ford and the dealer stand solidly behind the car. Everything of importance worked perfectly. Brings back all the memories. I look for excuses to drive and listen to that exhaust note. Couldn't be happier.