A major problem I have with my Elise is the lack of a proper emergency spare tire. The can of Fix-a-Flat in the trunk as supplied by Lotus leaves a lot to be desired especially if you are far away from home or a repair shop and you end up with a blown and shredded tire. After much time and research, help from a fellow LTer (thanks Cegan09), and chasing parts down, I finally have a viable spare wheel/tire in the trunk of my Elise.
The photos below show the marriage of a collapsible spare tire from a Porsche mated to a front base Lotus Elise/Exige wheel. As you can see from this first photo, in the collapsed state it fits perfectly in the trunk of my Elise even with the Sector 111 bootie and all the carpet and padding back there.
Here is a side view showing how much extra room is available around the wheel and if the spare is installed upside down, you can store things inside of it.
Here are photos of a collapsed spare next to an inflated one. You can see how much they grow when you inflate them as well as how strange they look.
The only drawbacks I can see are the loss of some trunk space, and the need to carry a small 12V plug in compressor as well as a small jack and a wrench to deal with the lug bolts. Also if you are weight conscious, this assembly weighs 31 lbs. These drawbacks pale considerably in my book compared to being out on the road miles from anywhere with a shredded tire and hoping to find a towing service that won't damage the car. At least with this set up you can change the tire and drive the car to the nearest repair shop. The top speed for these tires is 50 mph, but I read of a guy driving his 911 over 2,000 miles on his spare at 65 mph over the course of a week before he got his tire replaced. I wouldn't recommend doing that, but just being able to drive to a repair shop or back home after a catastrophic tire failure works for me.