The proper way is to copy the content folder to a Memory device that can be used from the official dashboard, then running disc2 like any other... "install" discs doesn't work when run extracted (normally anyways, maybe GTA V does? idk... but it's a waste of time and space!)
It's not a rumour by ppl that don't know how to do it, it's from ppl like me that know what the hell we're talking about, the Xbox 360 dashboard DO NOT read content from USB: it does however read from USBMU:Content000... there's a difference between the 2...