I just don't see how you're going to mount some of that stuff, like the power supply, without adding a side similar to what the case would provide for it to screw into. Even then, depending on the PSU, the vents are on the same side as the screws, which wouldn't end well. Then there's the issue of how to provide stability for the video card. It really needs a second side to connect to other than the motherboard for stability. Same issue, the screws are where the desk would be, which would block those ports.
The only way around it that I can see would be to carve out the desk with a router to fit those parts like the backside of a PC would, but then you would have to put the motherboard on the side.