I came up with a 'theoretical' solution as I plan to replace the wheels and tires at the end of summer. The performance tires I plan on are not run flats like the stock tires. On my 2nd day of diving the Bolt, a bolt (literally) punctured one of the tires and stuck in it. The stock Michelin did not lose air, and I was able to get the tire patched with no issues. So I see the risk of having no spare. Like you, I want to utilize the dead space.
Here is my plan.
A.) Purchase a 15" Space Master Collapsible spare tire & wheel like this offa eBay ($100):
This one came from a Audi, but there are others from Porsche and Mercedes as well. Obviously this isn't the correct 5x105 bolt pattern needed.
B.) So I will ship the wheel/tire to a machine shop such as Jason's in Chino, CA
that performs what is known as a "Fill & Drill". This process will weld close the existing holes and drill the proper bolt pattern ($100 + $60 to ship both ways).
C.) May need to jerry-rig some spacers or some mount mechanism so the wheel doesn't rattle around in the area.
D.) Will need a 12V portable high pressure (100 PSI+) air compressor ($75)
(this may be tricky as the high pressure ones often must clip to the car battery and not a cigarette lighter)
Edit: E.), D'oh...need a lug wrench jacking device as well.
I encourage you to test out my 'opensource' solution first if you so wish (at your own risk), and let us know if it works. :laugh: Otherwise wait around a couple of Months Months and I will try it myself.