So, yesterday I left the ACM-2 and ACM-3 at my office, since they were obviously sagging. This morning, as I prepared for work, I grabbed a small phillips screwdriver, a pair of tweezers, a box of x-acto knife blades, and two q-tips. It's slow today, so I broke out the ACM-2. Since I might have to put them up in a hurry, I resolved not to take the mics completely apart -- I had to sever the attractive yellow tape holding the inner protective screen in place (probably not a good move). I unscrewed the top clamp plate about halfway, and the ribbon fell away, resting on the bottom plate. I managed to fit the q-tip over the ribbon tip without completely removing the top clamp, then pulled the ribbon out and down the top side of the clamp unit ("top" meaning the part of the mic that's on top when it's positioned right side up, which it wasn't), and then screwed back in the clamps. I may have made it too tight, because there's not much corrugation showing, but it looks a lot better than it did. I put the yellow tape back in place but it sort of wants to peel up from where I cut it - oops. Hopefully not a big deal.
Next, the ACM-3. This one was a little tougher to get apart, but I managed to do so without unduly damaging the yellow tape. I halfway removed the clamp, only to find that in this case, the ribbon was indeed fused to the top clamp. As I "coaxed" it off with an x-acto knife blade, it became clear that it stuck on the edges of the clamp piece, but not the middle. I did slightly damage the ribbon at these points, although I suppose it was really the fusing that caused the damage. It was still in one piece. I had to completely take off the top clamp piece then, because the damaged portions of the ribbon had a tendency to catch on the bottom clamp as I pulled it taught with the q-tip. With the top gone, I still had to moisten the q-tip so that it could pick up the ribbon a bit, but I was able to ease the damaged ribbon over the bottom clamp to the point where the tension looked good, and the damage would be completely inside the clamp. I then replaced the top clamp, leaving a fair amount of corrugation -- looks much better now, and the damaged portion of the ribbon is indeed completely inside the clamp (and also hanging out the other side, I suppose).
We'll see how they sound

-- anyway, don't know if this will be encouraging (or tragically emboldening) to anyone, but I should say that I've never done anything like this before, and felt a little stupid trying it. Maybe premature to declare victory, having not heard the mics, but I should thank tarnationsauce2 for the incredible pictures and discussion from everyone. I tried taking pictures, but my cameraphone is so blurry that they're just irritating -- wouldn't have added any value to what tarnationsauce2 already posted anyway -- thanks!!!!
edit: they sound good! I did go back an de-tension the ACM-2 a little, which was dumb, because I wasn't paying enough attention. I wound up getting one of the clamp screws stuck under the motor assembly and ribbon, held fast by the magnets -- let the ribbon flop out and pulled out the screw/washer with tweezers. Even after that, no ribbon damage. For us newbs, it's important to realize that those magnets are strong, and that we're generally working with ferrous tools (screwdriver, tweezers, razor blade) that get pulled to the side very easily)