You can just use redsn0w 0.9.10b3/4 then go to "Extras" then "Custom IPSW" and choose the original 5.0.1 IPSW. redsn0w will automatically build the no BB firmware for you.
When you go into iTunes, hold option and click restore, choose the no_BB IPSW file and restore.
After phone has been restored, reuse redsn0w to jailbreak.