Press and hold the home button in the game (the one that turns green). While holding it, press the home button on your device. The game will exit but when you come back the door will be open. See related link for screenshots.
Tap the door 12 times quickly You have to morse code SOS on the door. Do 3 fast taps on the door, then 3 times slower, then 3 fast taps. See related link for screenshots and for a video guide showing how this can be done.
By tilting your device, move the can in front of the door, then tilt your device toward you so the can moves TOWARD you. Then launch the can into the door by tilting your device away from you. See related link for screenshots.