the boot lid trim has a small removable panel that allows you access to the actuator.
you will see a lever on this mechanism that allows manual locking/unlocking of the boot.
You might have to crawl in through the back seats though to do it though. I'm not sure that the lever will stay in the lock position after the boot has been shut. Though you could try lifting the boot handle as you close it? The same as you would with a regular car door.