the rig is tidy and clean as it is. If you're looking to do cable sleeving, I would instead just get extensions. FrozenCPU.com is where I mainly go for those but I believe Specialtech.co.uk will be better for you.
I've just thrown in the R3 fan controller, i am too ashamed to post the pic of how untidy the inside of the rig looks now. However running the system fans on quite now, much better.