[knc1]

That sounds right, did it work for you?

- - - -

One point about the terminology -
That is "USB Storage Mode" not "USB Downloader Mode".

I.E:
Export the Kindle's user storage area in the "mass storage mode" usually used to transfer books (and files) from the PC to the Kindle.

Transfer the **contents** of ... to the root (top most) directory of the user storage area as seen by the PC.

From the internal file system view given over the serial port, the top most directory is known as the path: /mnt/us/

In that directory (I.E: cd /mnt/us/ ), as the user named 'root' (which you should be over the serial port), with the Kindle running in the 'Main' mode (not in 'Diags' mode), execute the script named: jb.sh

The above (or something very similar) should do the trick.
I probably left out some re-boot and mode switching (the Kindles are dual-boot systems) in the above.
Just fill in the details I skipped over.