It must be possible to get to the back of the release by pulling off some trim on the inside of the boot. However, Honda must assume that the cable is very reliable as there's nothing in the Mk 3 Jazz handbook about emergency access to the release. This is in contrast to the Mk 4 Jazz where the latch is part of the electric locking system and there's a page in the handbook explaining how to unlock the cover from the inside of the boot.