These are what you have to do.
1. Rename the 1.1.1 firmware file from .ipsw to .zip and extract it somewhere
2. Go to that folder and look in Firmware->dfu and find the file that begins with "WTF"
3. Get iPHUC for your Mac or Windows
4. Connect iPhone to your computer. If iTunes opens, close it.
5. Open iPHUC. You should get a normal prompt. Type "enterrecovery" without quotes and hit enter. Your phone should go to recovery mode now.
6. Close iPHUC and open it again. It will have a recovery prompt now.
7. Type "filecopytophone <path to WTF file>" and hit enter
8. Type "cmd go" and hit enter
Now you can open iTunes and do the usual downgrade and get good old 1015 error.