Found the following online. Check page 12:
USB Flash recovery from Uboot
The info is for a "sheevaplug dev kit". However, I suspect it can be adapted to things like the GoFlex, Stora, and other such things.
This of course, assumes that the Dev Kit is similar enough to the finished product. IE, that the commercial version didn't change anything major in the recovery process - I suspect this is a very risky assumption to make. It would help to be able to get the original recovery file to examine.