I created a new page in wiki:
I also uploaded the necessary 945Byte with the MBR, Stage1 and a faked MAC-address.
Don't simple change the MAC - the kernel bootcmd is protected by a check sum (you need fw_env.config to change the mac).
This way works with disk of every size an disk of every vendor :-)
I tested the full script successfully with three disk (250GB Maxtor / 500GB Seagate / 1TB WDC)