You have irrelevant questions (i.e. 'are the lights on in the room?'). Forget those.  You have control questions (i.e. 'have you ever told a serious lie?).  Those are the ones you want to increase your physiological response.  Shit, anything will do.  I gave a light gasp and flexed my anus on those.

The point is you're SUPPOSED to lie on those.  They give you some bullshit spiel about how they need someone with integrity and if you ask for clarification (because EVERYONE feels like they told a serious lie, but what constitues a lie serious enough to disqualify you from being a cop?) they intimidate you into saying no.  I pretended to let my examiner do this.  I bantered back and forth for a bit, then acted worried and said "no, I've never told a serious lie". "Just yes or no, okay?" "O... Okay..." It convinces them they have you under their thumb when really you're sitting there laughing internally at how duped they are.

Anyway, you can recognize the control questions because they're vague and loaded and the examiner places the emphasis on integrity if you ask for clarification.  Just work on internally speeding up your heart rate and hit the response on those questions and you'll do fine.  If you're worried about your own nervous reaction when asked a relevant question then work on that other stuff like counting or whatever.  Just be confident in your skills.  You can only tell on yourself.