Mac Pro :: How Could I Power 2 Graphics Cards In (First Gen)

I'm currently working on completely migrating from my PC to my Mac (having kvm switches here and there has got very tiresome and I'm now very much restricted for room.) So I've set up boot camp and I am able to dual boot between OS X and Windows 7. I have two graphics cards currently sat inside the Mac, 1 ATI 4870 which I use with Snow Leopard, and a GTX 280 (which I've pulled from its water cooled environment in my PC) to use in Windows.

Now the problem, I use OS X exclusively for productivity apps like FCS3 and Adobe CS4, and wish to use Windows preliminary for recreation and games, which is where my GTX280 comes in.

Currently I have both cards in the machine, naturally OSX doesn't detect the 280, and I am fine with that. In windows I am able to utilize both cards, Windows detects both cards, installs drivers for them and works no problem running games on either card (preferably the 280 as it's relatively more powerful)

But that's with the aid of an additional PSU to separately power the 280 as the 4870 uses up both of the 6-pin PCI-e sockets on the Mac Pro Logic Board.

My real question is, am I able to buy two 4-pin molex y-splitters (still allowing the power to the DVD ROM drives), and then using the spurs to connect those to a '4-pin molex to 6pin PCI-e connector'; with addition to getting two 6-pin PCI-e Y splitters and connecting the 2 spurs to both the 4870 and the 280 via 6 to 8 pin PCI-e connector? -- Yeah the 280 is a power hugry card!

I've contemplated this myself knowing that the Mac Pro as a rated 1KW PSU, what concerns me is the PSU rails. Even if I can get these connectors to wire up the 280 with the built-in PSU, I don't know if the PSU's rail's will be able to provide the current required.