I did the same thing years ago with the open and closing mechanism out of a broken DVD player . But I put 2 peices of 3/8 steel square tubing on both sides of the door and upgraded the motor to push a flat peice of stock 3/8 steel back n forth.
so the on switch is just so you don't waste battery or? cuz im guessing the remote is to activate the opening and closing but could you do something similar but have a one and off switch at say a desk across the room and have it be able to unlock the door still?
you can easily take off the battery, it may leave a rip in the cardboard but you can simply cover it by hot gluing another one then reconnecting it to the lock