How can I completely close a vent in my house?

I live with a couple roommates and they don't want the A/c on no matter what. Even when the temperature is over 100 like it is today. How can I close the A/C vents in their rooms so that they get no cold air,when I want to use it. this way I will pay the amount that is more than our usual electricity bill since I will be the only one using the A/c. my idea was to duct tape them ****.