I think you need to do that:
Download and extract the root filesystem tarball onto the new ext3 partition as the root user, not just sudo. Create a file at /usr/local/mac_addr and place in it your Pro's MAC address (its on the bottom of the unit) in the format XX:XX:XX:XX:XX:XX. Safely umount the drive from the computer, plug it back in to the powered-off Pogoplug, and then plug in the Pogoplug
You prepare the work from another pc, power off the pogo, plug the usb key, power on...
So no ssh to pogoplug is required.