You'd have to be more than a mere passenger. You'd need to know that the driver was above the limit and you'd need to do or say something to encourage the driver to drive.
If the driver says 'I'm going that way, I can drop you at your house' and you agree to the lift, you won't commit the offence because you've done nothing towards causing him to drive. On the other hand, if you persuade a drunk driver to drive you somewhere, he being reluctant, you saying e.g 'Go on it's not far, you can risk it, all the buses have gone and I need to be home' then you'd certainly be committing the offence.
People do get charged when they are passengers but mostly these are extreme cases, drunk youngsters encouraging one another to race in the streets etc