I've only read the first 4 pages so maybe this was mentioned already, but it seemed no one said anything about self-hypnosis. It's rather similar to meditation, only more focused on a specific goal, like being able to hallucinate in a controlled manner (whenever you clench or hands or something like that). Like meditation though, this of course takes quite a commitment and isn't something you can just do in a week or so. However, if you put the time in it's possible to just point at a brick wall and say "That wall is green" and suddenly see it as green.
I've tried this a bit, but I'm not nearly that far. Google has a lot of good information if you want to know more.