Yeah there is no adjustment for rear suspension per se (the ti uses the E30 rear suspension, like the Z3). A 4 wheel alignment is really only checking your rear. Aftermarket kits replace your 4 trailing arm bushings with the bolt offset vs the radial center of the bushing. When the outer bushing is rotated relative to the inner bushing, each corner's camber and toe are changed simultaneously. It's not an ideal solution, obviously, since you have to pick one variable first (generally toe) and settle on the 2nd variable. It's a constant tradeoff, but it will work just fine for 99.99% of drivers.
I use a KMAC adjustable rear bushing kit for my 88 M3 and it works great. The ti's alignment is fine now so I'm not going to spend the $ to solve a problem that doesn't exist.
If you want to delve deeper into the bushing solution, check out Gustave Stroes' explanation
here .