I suppose a baseball bat is out of the question.....
As for someone who sat at the lights clearly not paying attention - a quick beep on the horn. If that didn't work then a longer one. After that I suspect you have to assume that its an obstruction that isn't going to move, broken down or even driver taken ill - pass with caution.
As far as the ambulance is concerned, they are trained to wait at the lights behind as they are subject to the same law as you, although, I have before moved across the line to create space for them to pass but never crossed the junction. If they're in a real hurry they will pass on the wrong side forcing traffic to stop if its safe to do so. Am sure, if they're aware there's red light cameras that they wouldn't force/induce a driver to cross the red light.
It does't help though if they're sat there behind you with siren on - thats intimidation.
With police its even more difficult - How do you know they're not an armed response vehicle. I would hope that if you did end up with a ticket in such circumstances that if you had been forced/intimidated into breaking a red light that you would get the police support - they would't want the bad publicity of forcing an otherwise law abiding driver to break the law and then not support them - especially if its on video...