I believe something like this could be possible using a TeleportPlayer(string & asStartPosName); you would probably have to make a duplicate of the hallway and edit it making it longer or shorter and scripting it so that when the player reaches the end of the hallway it teleports them to the the part of them level with the shorter hall, and all of this can be done in the same map.
I hope this helped
EDIT: also check out this website for other scripting help
http://wiki.frictionalgames.com/hpl2/amn...ne_scripts