If this is the only major obsession (outside of the bikes) I wouldn't worry too much about it. Is there anyway to get outside without having to deal with this door? Otherwise, maybe try distance training. Start him far away, have him sit/stay, and the door opens. Gradually do this and move him closer and closer. However, maybe working on basic training in general would be good so that he follows "quiet", "wait", etc. in various situations.
