I did something similar once before. I flashed a linux loader rom (basically the same thing as cromwell) to my tsop. It was a bitch to get it right
again. What you need to get is something called the eurasia flash disc. I think it is the only thing that can save you now without buying a chip. Google should help you find it. Burn it to a CD-RW very slow.
I am a little fuzzy as to whether the disc booted or not, I can't remember. If it doesn't boot, then you will need to try option 2.
You can extract the eurasia flash disc ISO and put those files on your xbox HD (on the root of E Drive) so when your cromwell starts up you can select the FATX icon and boot eurasia.
Hope this helps