That sounds confusing. What do you mean? My usb cable comming out of my screen is at most 4 feet long and is only about a foot long out of the vga connector. I wouldn't think you would gain anything by cutting anything there... unless you have a super long lilli or xenarc cable or something that I'm not familiar with.
I would just run a usb extension up from the back to a powered up in the dash then plug everything into that hub... no cutting... everything is reusable in the event of car pc removal.
Maybe I'm way off what you mean... if so... sorry