User blog comment:Damac1214/Black Ops II Zombies Reveal Released/@comment-3046261-20120926234316/@comment-1854594-20120927025734

If you have an Xbox (don't know if you can do this on the other consoles) it's as easy as plugging in a usb device with the song you want on it in mp3 format. For PC you can just have the song running on the computer at the same time.