Simplest way is to turn off bluetooth pairing and plug it in to the usb port. Or put your music/books on a usb drive and use that instead.
But I don't understand the advantage. If the phone isn't connected to Sync then it can be used like any other phone. At least with Sync you get hands free operation and voice commands to make calls, have texts read to you, etc. which I think is much safer than using the phone stand alone.