I like the suggestion, will be fun, but what, you'll play this for like 2 hours and never play it again. I don't understand why this is so important...
Otherwise, to fix the GLaDOS hanging from the ceiling, use the Model for GLaDOS as a bt playertype but extent the collision box down so that it touches the ground, but GLaDOS isn't.
Problem, with the Portal Gun in the presence of GLaDOS, any player can portal a wall and the ground under GLaDOS and portal her somewhere around the room anywhere they like, so use Non-Portalable surfaces in GLaDOS' presence and clear portals when going up to the next level.
Other than that, OP needs patience.