Yes you can do the firmwareupdate on the regular memory of the pocketbook, the best way is to charge it while doing.
To do so with USBcable, go to the settings->USB and choose "Ask when connecting", than you choose at connection to only charge it.
Copy the file to the root dir and do the steps described above
I also did it like that, but without charging it during this process, this is a lil dangerous, but not that dangerous, if your pocketbook is fully charged