The way most dome lights work is the bulb always gets power and there are several ground wires at the doors that connect to switches. When the door opens, the switch closes allowing the electricity to flow to ground. This completes the electrical circuit and the light comes on.
You can disconnect the wire that goes to the door if you never want the light to come on with that door. You could also put in a type of latch that would keep the door switch from coming out when the door opens. or put a switch inline like HDR suggested.