Seeing a thread earlier today about a rear-strut bar made me think of this. So far, it's the only product that seems to work for our particular cars (tower-mounts are questionable for the ti), and doesn't give up any hatch space in the process. There are testimonials at the bottom, and more information can be found at the following sites:
z3roadster.net roadfly (NOTE: in both instances, the strut was installed on an M Roadster. Tightening up that car takes some work, but this product seems to do it.)
Sent a message to Paul earlier today, and got a response within hours:
5 units at @ $320
6 to 10 units @ $300
11 to 15 @ $280
+Shipping (see below)
Unfortunately, this is not a huge discount, but it beats throwing your money away on a product that doesn't really do anything.
Shipping to the US is $15 on top, to Europe is about $43. I have given Paul a timeframe of the end of March, so please reply to this thread with questions and interest (please put it in bold, and I will later add your name to this post).
Product information here:
http://strong-strut.com/Butt-Strut.htm