Quick report: I was able to fit a BMW space saving spare under the regular trunk of my M40i. Here's how. First I removed the trunk floor. There are 4 torx screws underneath that hold the hinges together on each side. I put the tire down and drew a circle around it. I used a utility knife to cut out a generous hole in the subfloor--which I figured would help keep the wheel in place.
Now I see why they raise the trunk. The tire really doesn't fit longways between the metal frame behind the second row and the battery at the back. The tire is a looong 26" and the space is a short 25.5". And that was the toughest part. I won't go into every thing I tried. I'll just say it took me the better part of the day to figure it out. I took about half the air out of the tire and jammed it in.
Anyway, I wrapped the the jack and put it horizontally in a sunken space right in front of the battery, beneath the tire. The rest of the goodies went wrapped in the space saving wheel well, including 2 emergency chains that I can put on on a stuck tire, without taking the wheel off. Put some padding on top in case I wanna drive like an nut so things don't bounce around. Put the trunk floor back on and shut it all snug.
(I ordered separate from getBMWparts.com and boy it still ain't cheep) Note: I did get the jack carrier, it wound't fit vertically.
Sorry for the bad images: don't know why they're coming in sideways... but you get the idea.