How to unjailbreak but...

Yes, you can restore with an .ipsw file without baseband and with stiched SHSH blobs. There are several threads here giving details, and probably a tutorial on iClarified.com

Just be absolutely sure that
1) You have the SHSH blobs for 5.0.1 (otherwise read them off the phone with redsn0w or iFaith)
2) That you make a custom IPSW without the baseband.
3) That you stich your SHSH blobs to it (redsn0w or iFaith)
4) That you do not point to Cydia instead of Apple in your computer's hosts file (TinyUmbrella will do that, unfortunately. It was a good idea with iOS 4.X)
5) That you put your iPhone in "Pwned DFU" mode before restoring the custom IPSW (redsn0w or iFaith will also do that for you).

Good luck. I hope I did not leave out something essential

 

You need both 5.0.1 hash file and the APTicket to stitch to the No_BB IPSW
Once you stitch these to the IPSW, the host file is irrelevant, the authentication iTunes requires is built into the stitched IPSW.