You can do it via unlock or root, but you don't need both. As far as I'm aware it's not able to be flashed without one or the other. Unlocking is easier than root, though likely slower due to it wiping your data. I went with unlocking because I prefer to stay stock and wiping data before a large update is never a bad idea anyways.
For unlock follow these in order:
http://androidforums.com/verizon-ga...gs-root-samsung-galaxy-nexus.html#usb-drivers
http://androidforums.com/verizon-ga...s-root-samsung-galaxy-nexus.html#adb-fastboot
http://androidforums.com/verizon-ga...-things-root-samsung-galaxy-nexus.html#unlock
Then grab:
http://download.clockworkmod.com/recoveries/recovery-clockwork-5.5.0.4-toro.img and put it in the same folder as fastboot on your computer.
Load the leaked files onto your phone's root directory.
Plug your phone into your computer.
Open a command line at the location where you have fastboot and clockworkmod.
Type: fastboot-windows.exe boot recovery-clockwork-5.5.0.4-toro.img
That will load clockwork on your phone without flashing it so you're still 100% stock.
In clockwork you'll want to select "update from sd card", likely browse to find the file. Flash IMM76Q and then JRO03O.
When you're done just go back on the menu until you get the option to reboot your phone. Simple!