So you want the latest version of Jelly Bean, but don't want to wait for your turn at the OTA and don't want to flash a custom version of it. We completely understand -- Not everyone is into that. The good news is that a little bit of hackery (just a little, we promise) and an unlocked bootloader can get you some tasty new Jelly Bean with no wait. And when you're finished, you're good as new and completely stock.
Next you'll need to find the folder where your fastboot installation resides. Place the ClockworkMod recovery image file (it has a .img file extension) in the folder with fastboot. Copy the OTA package zip file to the storage on your phone. Shut your phone off, then hold both volume up and volume down, then press power to enter the bootloader. Now follow along!
Plug your phone into a high-speed USB port on the host computer.
Open the command line on the host computer, and browse to the folder where fatsboot and the ClockworkMod image are located.
At the command line, you're going to tell your phone to reboot into ClockworkMod. You're not going to flash anything. If you're running windows on the host machine, type in fastboot-windows.exe boot recovery-clockwork-22.214.171.124-maguro.img . If you're using a Mac or Linux, type in fastboot boot recovery-clockwork-126.96.36.199-maguro.img .
Your Galaxy Nexus will reboot into ClockworkMod recovery, where you can follow the on screen instructions and flash the OTA package you downloaded and copied to the phone in the beginning of this procedure.
When you're all done, choose to reboot your system from the ClockworkMod recovery menu. You will boot normally, into Jelly Bean, and since we didn't flash CWM, you're still 100% stock.
It looks more complicated than it is, but if you're a bit put off or having trouble unlocking your bootloader, head into the forums. They'll fix you right up, and have you rocking some Jelly Bean goodness in no time. Ummmmm, Jelly Bean.