I don't know exactly where the thread was, but it was pretty much just brought up and dropped (with a little discussion of thermodynamics). Someone said that the one-way mirrors used in interrogation booths required darkness on the non-reflective side, but that's obviously not the case for whatever's used for mirrored sunglasses. And no one responded to that. Maybe DarkStorm knows where he could get his hands on such material. Or maybe someone could grab an old pair of mirrored sunglasses (they're probably still in the pocket of your Members' Only jacket) and test it out by just removing the current lens and holding them up to the VFD.

Edit: Here's the thread