Stand at the entrance to the elevator when the button is pressed and the door closes. The door will then be caught in the door and the player's position will change. Then, when the elevator descends, the player can skip the floor and skip the events and movie that immediately follow.
See the video below for more details.
However, I have not yet found the setup for this glitch. We would like to find a stable setup, as it will greatly reduce our time.
I think I found why I "teleport" directly into the last room since I managed to do it multiple times in a row but it's still a bit random. So I think I'm going to try in a run to see if it can even work with a new save. And as far as I can try I think that 300 fps is a good framerate to clip consistently in the elevator.