The boot release is electronic, if the doors are not unlocked you cannot open the boot. Same for the central locking, and if the OP had deadlocked the car, you would have no chance. Im not sure what your getting at.
The OP metioned the were several cars done, my suggestion was a fairly universal way it could be done - I dont know about the Grande punto specifically.
I assume if you open the drivers door for instance you can open the boot - or does the car ignition need to be on to open the boot??
