I'm not actually sure of what you mean by 'directly' here. Which of the following does 'setting up the preconditions' include:

a) changing breathing patterns etc b) focusing thought on particular events etc. c) rationalising consciously about your emotional state d) thinking something like 'calm down, DavidAgain calm down calm down'

I doubt many people can simply turn a powerful emotion on or off, although I wouldn't rule it out. I read (can't find link now...) about a game where the interface was based on stuff like level of 'arousal' (in the general sense of excitement), which you had to fine tune to get a ball to levitate to a certain level or whatever. I'd be surprised if someone played that a lot with high motivation and didn't start to be able to jump directly to the desired emotional state without intermediary positions. And being able to do so obviously has major advantages in some more common situations (e.g. being genuinely remorseful or angry when those responses will get the best response from someone else and they're good at reading faked emotion, or controlling panic when the panic-response will get you killed)