Oooooooo, I gotcha now.
Yes, all other BMWs I am aware of use some kind of mounting bracket that does not intrude into the cargo space. However, I have never seen a changer in a ti, and I don't know if there is a factory mounting point or not.
On any other hatchback I've seen, its always bolted to the floor. What I suggest you do is go to the good ole home depot, find some solid brakets and steel or aluminum (if you can cut it, if not, use wood) and fabricate a mounting bracket on the bottom of the rear shelf.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>