Thanks for the idea of using the weight of the car to my advantage. Seems obvious now...
I too have much more experience with MacPherson struts, where you always have to remove the springs...

As stated, I can see how if you are not interesting in removing the control arm itself, you could simply leave the spring in place, and under compression (with some of the weight of the car remaining on it), and still be able to replace the struts and the balljoints. This is a great shortcut.

If you actually wanted to remove the spring (no choice, my bushings were toast), I would be concerned that the spring might pop out of its mounting on the control arm end before the pressure was entirely released, due to the severe angle. A solid clamping to the arm could prevent this perhaps, but spring compressors would still be safer.

The hardest part of this job for me was removing and installing the springs with my standard bolt-type compressors. The biggest problem here is that only a short segment of the spring is accessable for clamping, so it is difficult to compress it enough to remove and install it.
Since my friend's control arms really do have to come out for new bushings, this will be the modified technique when we do this on his 300E next week:

1) Place jack under control arm and lift until all possible weight is on it. Lift fairly high- you will need extra downward travel later.
2) Place jack stands under frame (for safety-weight stays on jack for now).
3) Attach spring compressors (the cheap bolt-type are only about $10), and tighten just until taught. This way, the spring pressure will release before it is fully-extended, which should be both safer and easier.
4) Loosen eccentric bolts (control arm to frame), but leave in place for now.
5) Remove bolt that clamps steering knuckle onto balljoint, and pry open the split slightly to loosen.
6) Slowly lower car onto jack stands, and continue to (very slowly) let control arm drop. Strut should bottom out first, balljoint stem should slide out of clamp (warning- this may need some "persuasion" to get it started), and eventually the pressure on the spring should be fully released. Having the cheap-style compressors in place should substantially reduce how far the arm needs to drop before the spring is loose.
8) Now, everything can be removed as needed.
7) Installation is reverse of assembly (as they say)...

This is going to be much easier next time- thanks again for the ideas...