This is what I use with my CEC transport and it works better than all the other gadgets I tried :
A Herbies Grungebuster SP (self adhesive) CD Mat adhered to the bottom side of the puck.
Also, a Van Art Speak "De Mat" is placed on the CD itself before playing.
Note: If you have a drawer-type front loader, I would suggest using one of these products, not both at the same time, also read the link about the De Mat at Globe Audio Marketing Inc. they explain its usage and applications quite well.
See what works best for you and your equipment, I only did this because I came up with the idea of combining the two together for extra mass and coupling and got lucky.
The De Mat is a flexible rubber, carbon fiber embedded composite that has a small "lip" on the outer edge to help aid in self-centering itself (covers the edge of the CD)
You can order these from Upscale Audio or Globe Audio Marketing Inc.
I get way better dynamics, separation, smoothness and detail with these in place, your mileage may vary.
The problem I found is that CDs are NOT cut to the same outer diameter, which is a pain in the butt, because if the CD is slightly larger, the De Mat will not lay flat on the disc.
I would like to find a safe way to slightly trim or sand the outside edge of the CD, so they are uniform to one another in circumference.