I have an idea that could give the illusion of a pull down ladder.
Make the brush thats you want to be the ladder, a func_train, and set that up.
http://cariad.co.za/twhl/tutorial.php?id=10Basically that but change it to fit your needs.
Then make a very thin brush infront of the ladder but make it completely transparent.
Once the ladder has come down, you will be able to climb up the transparent laddder in front of the fake ladder which is a func_train.
I hope that works......