I know it's cheating but buy some 12 inch extensions and connect your PSU PCI-E cables to them. You can still sleeve everything and hide those extra connectors in the back of course it'll look far more seamless that way. What are you planning on sleeving the cables with? I use paracord, heatshrinkless method which is a pain but looks very nice when finished.
"People willing to trade their freedom for temporary security deserve neither and will lose both." ~ Ben Franklin