I didn't, I found the the sled rested alot on the AC controls below so there was little need IMHO.
But, I did find something back there that was useable when I was orignally planning on supporting it. If you look at the third picture you can see some white plastic in the back, this is the AC pipe that feeds the center consol vents above the DIN slot. It has two bolts which are hidden in the photo behind the AC controls, but they are just about reachable, and I was planning on use two stiff metal strips to run from these to the mounting bolt.
But due to space considerations, haha, and the support from below this idea was nixed.

I like your idea for the stealth cover, but current plans call for the radio to return to it origanl place. But I'll keep my eye out for one - the shine from the sled does make it noticable that the radio has been removed and that there is probably epensive stuff worth nicking in the car.