Step 1) Buy any 6850, 5850, 6850, or 460GTX card
Step 2) Buy Accelero S1 Rev 2 cooler
Step 3) Buy a very quiet fan like a Nexus or Noctua
Step 4) Buy a fan controller or at least one of those connectors that can put the fan on 5v, 7v or 12v.
This takes up a ton of space inside the case, as the Accelero takes up space, then you zip tie a 25mm thick fan to it... but if it's all you need in the case, it's QUIET. It's not passive, but I cannot hear the one I did for my 4850 when I'm three feet from it. When I did that on my 4850 I not only had a cooler I could not hear, I had a cooler that cut temps over ambient in Furmark by HALF and allowed more overclocking headroom than anyone else in the forums was getting with stock fans.
Come up with a scenario where you can afford to take up 3-4 slots with your video card and you can have most cards in there.
Fully passive is a joke. You need some fans in your case anyway. Get one on the CPU and one on the GPU, but make sure they're QUIET fans. It will be miles better than any passive setup.