The leader should also ask the group at the very beginning whether you are there at anyone else's request or for anyone else. You can opt out at that point too. As mentioned already, it's not easy to stand up in front of everyone and leave, but I have seen it done.
You could also review the Landmark disclaimer - if you have every had anything that could be considered one of the conditions which Landmark themselves say mean you should not take the forum, use it. This could be a get out clause. Your employer will not want to be sued for you being harmed as a result of them forcing you to take a course that the provider clearly states is not for you.
If there really is no other way but to sit through the 3 days, get as much sleep as possible, turn up late (towards the end of my Landmark days I pretended I was having "completion conversations" outside the building while all the time chatting to my friends - the staff never interrupted me), take frequent breaks (you could invent an appropriate medical complaint that means you have to go to the toilet often) and do NOT do the homework. If you can, arrange to meet friends or go shopping during the breaks (they strongly encourage you to spend this time with the other participants). Above all else, SLEEP.
A couple items about hypnosis. Hypnosis has been shown to only work where someone agrees to it's purpose. The "processes" are framed as resulting in people getting what they want so people will follow them. If your conscious of the methods, it's much more difficult to have you follow them. A method that has shown to work in countering hypnosis is when directed to think of things, think of different things on your own. Imagine your own outcome and make your own thoughts about thing like what you'd like to do next week can make the hypnosis ineffective.