This is the way everyone is doing it or trying, but you need to unlock the skill and wait the right condition. In this case you have to do the mission the way you say on the video. I still thing the way I show is easier and you can do it wherever you want and whenever you see the opportunity. You don't have to wait or create the right opportunity, you will find a lot of enemies climbing a ladder. No attachments to skill, nor missions. Also, you can create the situation where an enemy climb a ladder. But, it's ok. The important thing here is to get the trophy and have fun playing the game.