Eh, I recently joined this forum, so I am not up to the speed
Out of ignorance I assumed that the actual upgrade file(s) would not be available to users, and instead it/they would be silently pushed through the kobo desktop app and the upgrade would be triggered by some command from the desktop app. Obviously, Kobo engineers came up with a better procedure.
Otherwise, I agree that the internal Kobo memory behaves just like any USB storage, so if he can get the actual upgrade image it will be trivial both to do the upgrade, and to add new books.