Well, I took the car to a local MB mechanic, and he says he also has no way to adjust the rear camber. I think at this point I will go ahead and drive out these tires and see how long they last. I kept my old springs, so I can have them re-installed if I decide to.

Clearly, lowering the car affects the geometry by creating negative camber. What have other folks done who installed the Eibach kit for street driving? I presume you must know what your post-alignment camber was, the same as me. Any tire-wear results with -2° or more of rear camber?

On a side note, since my previous tires wore out so fast on the outside of the tire, maybe having a little negative camber will balance it out. I can always hope so, anyway.