So is it a full or mini?
Taking off the right side panel and stashing the extra wires behind the mobo mounting panel has always worked for me. Sometimes the panel is tough to put back on, but anything is possible with the correct motivation.
Mini tower. I'm not at home right now but a rough estimate:
The motherboard is on the left side of the case, with maybe an inch between the metal and the MB.
The PSU is at the rear of the case, at the top, touching the top, with the cables dangling down to the bottom of the case. The space between the the MB and the right side of the case is about 6" or 7". Enough for a GTX 590 but just barely. I'll take a picture of it when I get home.
Basically there is no way the cables are going behind the motherboard, it won't fit. I think I'll just see if I can't tape it to the top.