If you have the highline computer on the GTi (if you have the gears displayed along the bottom of the display rather than up the right then you do) then you can go into the setup (press "up" on the button on the end of the right stalk for a few secs) and switch on auto door locking.
Its under Convenience, Doors, Auto Close or something like that. When you drive away the doors lock automatically, and when you take the key out the iginition they unlock. If you want to unlock manually, press the button near the drivers door handle.
Also, if the passenger wants out, he can pull the handle twice to open the door.
If you don't have the highline I think the dealer can do it for you.