"Sorry, officer, I don't understand your question."
"Are you paying to be a passenger in this vehicle?"
"I'm sorry, officer, I want to help you, but I just don't understand how this involves me. I'm just a passenger here."
Most cops will just give up asking the question there. If the officer pushes the issue, he's being an asshole, but you can still very politely invoke your fifth amendment rights: "Sorry, officer, I should have an attorney present to help me with these questions."
At that point, answers to any further questions (if any: standard police policy everywhere is to cease questioning immediately) are completely inadmissable (Edwards v. Arizona, 1981).
You can beat the rap, but you can't beat the ride: that's true. With that said, the cops who will bring you downtown for asserting your rights are exactly the cops that you really shouldn't be talking to.
(IANAL, FWIW; I'm just an occasionally rude anti-authoritarian citizen who has to mentally practice polite assertion of my rights so I don't accidentally piss off cops who, in their view, are just doing their jobs.)