[coreboot] usb stick payload?

[Motiejus Jakštys]

Hi,

I have thinkpad X60s with coreboot and with only one payload: SATA hard
drive. I would like to add a "boot from usb stick" option. However,
can't find the payload (i.e. source to generate the necessary coreboot
ELF file).

Wiki mentions that I need the coreboot payload ELF, doesn't mention
where to get it. :) I would appreciate some directions.

Thanks, 
Motiejus Jakštys