the first step is to make just a little bit of lateral space by removing the plastic brackets on one side of the drive cage, using a special right-angle screwdriver. you only need to remove one screw. (temporarily remove the front fan to make working room)

here is what the cage looks like with two of the brackets removed. note the small clips made of spring metal at the rear in the photo below, which were uncovered when the plastic brackets were removed. these are easily popped out with a small screwdriver.

i obtained some nylon shoe lace material and "cord locks" from a local outdoor-recreation shop. 10 ft of shoe lace and 4 cord locks cost about $3.00.

the next step is to cut a 24" length of lace, thread it through the drive cage, and add a cord lock. i heated an old knife on the stove until it was hot enough to melt through the nylon lace. this keeps the ends from fraying. a toothpick makes it easy to get the shoe lace through the cord lock.
the drive will go through the large opening in the lace in the photo below. when the lace is tightened, there will be a layer of lace between the drive and the drive cage.

a second lace is added, so there is one at the front of the drive and one at the rear.

the drive is now inserted and the laces are pulled tight and secured with the cord locks. it helps to do this in a couple of stages, tweaking the position of the drive.

at this point, you may be satisfied and go no further. i decided to add two 20" pieces of lace running lengthwise, for redundancy and to keep the drive from rolling on its lengthwise axis. these go over the top of the drive cage. tightening them has the effect of drawing the drive upwards, adding additional tension to the widthwise laces. the cord locks make it easy for you to make the whole system as tight or as loose as you like.

if you need to replace the drive, the laces and cord locks can be loosened, but they do not have to be removed to get the drive in and out.
it was easy to do one drive this way. i'm pretty sure you could fill the front cage with 2 or 3 drives, using the same technique. you'd thread the laces so the cord locks are to the left or right of the drive, rather than under. this makes them a little more cumbersome to tighten but is workable. i'm sure you could also get at least one drive in the rear cage with this suspension. more than 4 total drives might be possible, but would be tricky.
i have not yet evaluated sound or temperature. it may be a while before i get this system all together. the drive does feel like it's nicely suspended, and it will not make any contact with metal or plastic.