Its very straight forward like the above response plenty of tutorials on iclarified.
You will need your 5.1.1 shsh blobs - then cook yourself a custom firmware using snowbreeze and your blobs - restore in itunes using your new cooked firmware.
Redsnow the latest version does everything for you - so really you can use redsnow and skip the snowbreeze process...
I'm going to guess he doesn't have Blobs if that's the case there is no way!!! Once Apple stops signing it then it's to late you can use Tiny Umbrella or RedSn0w to check. info on that is again at Iclarified.