I used to do this, but without cutting them in half. Then, use the different hardness - blue/white/yellow/double yellow - and keep them from rolling around with a 1.5" neoprene gasket ring.
However, while they help some equipment, they made others lose tightness in the lower frequencies, and can sometimes even muddy the midrange. Then, I went to the hard-type suspension - Aurios, various spikes, cones, etc. Unfortunately, everything I tried has a characteristic "sound". I discovered this when evaluating two CD players - changing the rack/cone made more of a difference than changing the CD player.
Now, I use 3/4" thick or 1" thick high-molecular weight cell-cast acrylic. The same material that Clearaudio and other manufacturers use to make their megabuck turntables. Easily available at a store that make display and exhibition shelves, acrylic fish tanks, etc. At a place like Tapp Plastics in Seattle and San Francisco, they will even cut to size for you.
Replace all glass/mdf/wood/granite shelves in the equipment rack with a sheet of this.
Then, instead of cones or ball bearings, replace with the acrylic cabochons.
Tap Plastics even sell acrylic rods and tubes, and you can easily assemble a very, very
NEUTRAL sounding rack out of stuff you can get there. I emphasize neutral because you'd better like the sound of your equipment if you do this.......
ps. I have NO affiliation with Tap Plastics - except that all my experiments have been made from material I've purchased from their local store.