Thanks for actually giving credit wooden leaf. The only part required for that to work is something for the shield door to push the player against, and once he reaches the top, the force of the shield door will actually propel him over the ledge. You could just place the shield door in a corner so it's like a ladder and players can jump down anywhere else.
http://www.forgehub.com/forum/halo-reach-forge-discussion/111229-ladder-tut.html this is another idea you could use, basically a much easier version of sqorks ladder.