The only technique that will work is to have a poker-faced and it can be done by practice and through meditation, I have seen people who practice yoga and they can have no feeling or expression at all if they want, practice makes perfect if you practice over a thousand rounds and you get to use having no expression at all, you can achieve that if you are dedicated to your craft.
I still don't know what a poker face is, is not having an expression what is meant by a poker face? I didn't know there was this term but anyway, I don't think you should practice yoga because in this case at least you can control yourself, don't panic and can keep your breathing steady. So that way, I'm sure when you do it often you will also be able to apply an expressionless face in poker but still, it seems like it's something difficult in poker because the tension in the game is bound to happen.
I do not see a non-professional using meditation or yoga in order to play better at poker. I do see professionals doing it on a constant basis, because the sums of money they have to bet on are sometimes life-changing and it takes a special personality to stay there without blinking. I also wonder sometimes if they are able to lie to a detector or send a false signal on purpose to other players. And all that at the same time that they are watching the rivals while appearing not to be watching the rivals. Perhaps enough to drive anyone insane?