If u still have not got problem resolved I had a similar issue, I just wanted to update to latest unlockable BB not the latest BB and kept getting an error. Used this turtorial appears to me that it tricks itunes. Hope this helps... http://www.sinfuliphone.com/showthread.php?t=66225
All I needed to do was to click "option-restore" to select my own ipsw file --- once that was installed - I was stuck in restore mode at I was getting the 1013 error.
To fix that I just unchecked "set hosts to cydia" ---
Then I tried restoring again and this time itunes downloaded its own version and installed it successfully.