I don't actually go to meetups, but Harry's comments about anti-conformity training made me wonder if it'd be worth trying.

You could retest the original experiment, see if lesswrongians can avoid it through knowledge of the effect.

You could mock obviously true statements to practice withstanding opposition.

You could practice the ability to do harmless but nonconformist things to gain the ability to do so if the situation called for something unusual, but you might otherwise be too conformist or embarassed. (each meeting attendee shall order a coffee whilst wearing the ceremonial tea-cosy!). I suspect some of this overlaps with PUA a little and easily veers into general confidence building.

I don't know if rehearsals would do any good, but you could go through the motions of not complying with the Milgram experiment, making people handle little fake emergencies...

You could wonder if EY is planning things like this for the Center for Modern Rationality.