They can actually be added to stock deodexed roms as well. Just search "galaxy nexus soft keys zip themer" and you will find quite a few. Then you load the zip in Zip Themer which will create an install file for custom recovery.
Or just flash a ROM for more options. Can't go wrong with AOKP and CM9. CM is a bit more basic - AOSP+ if you will. AOKP is nuts on options. Soon you will be able to have Widgets in the nav bar as well as shortcuts on AOKP.
Then there are all the forks and custom builds of those so you may as well start now... FYI - you may have to visit meetings after you start...
Sent from my brain using human to phone transport technology.
FYI, if you flash ICSourcery there's tons of soft key mods inside the rom to install. But to add more, the options are usually in the rom tools in the settings menu. Or search my username for latest threads. I have a tutorial about them & some soft keys I made. And since some roms allow you to change them without installing anything, just download my zip, unzip them & let the rom tools change them for you.