First of all, there's no reason to lower everything at once on the rear end, even if you had incredible hulk-like muscles that could handle it. The differential alone without the axles weighs about 70 pounds. It's extremely easy to spin out the two 8 mm bolts that hold the axles in the hubs, pull the trailing arms only, then the diff with the axles attached to it.
Second of all, the mercedes shop manual has directions for lowering the arms, springs attached, without a compressor. I just did an entire front end rebuild without a spring compressor, and it was no big deal. The only tricky part is keeping everything steady while you jack the trailing arm back up into place. The rear springs especially have very little compression on them when the trailing arm is down on its stop after jacking the car, you can actually squeeze them a little with your fingers, not nearly as heavy as the front springs.
Third of all, before I started my front end rebuild, I bought one of the more popular spring compressors, as recommeded here. It broke. I'm not naming the brand because I'm sure it was just a defect, but since I lived through the experience I've decided not to spend much time around that kind of stored energy. Even the name brand compressors run a risk, I personally prefer the springs with as little pressure as possible on them. Letting my front end out was only about 3 inches after disconnecting the UCA. Good luck!