You should be able to do this:
Put the phone into DFU mode yourself by plugging it in to a mac and then turning the phone completely off. Then, hold the power and home buttons together for exactly 10 seconds, and then release the home button, but keep holding the power button. iTunes should then tell you that there is a phone in recovery mode bla bla bla. You should at no time see anything on the iPhone screen. Once you see the iTunes message, you can let go of the button.
Once you're in DFU mode, restore the phone using iTunes to the latest official 2.0 software. Once that's done and assuming it was error free, run pwnage. pwnage should do something to your phone (as in you should see scrolling text on the phone screen) and then reboot your phone. Once you create your custom firmware, restore it in iTunes.
If that doesn't work, let me know. You can actually revert back to 1.1.4 official and use pwnage 1.1 to do the initial "pwn" and then just upgrade to your custom firmware 2.0 afterwards. I did this on the weekend for a friend who accidentally upgraded to 2.0 from an unlocked 1.1.4.