You'd want to redirect the grounds from the lights to a switch. Find all the wires bolted to the body near the lights, those will probably be for the lights. Unground each one as you watch to make sure everything else works. Put them all to a 15A or more switch that connects them back to ground. Switch on, Lights work. Switch off, Lights out. I've heard it'* better to use a 30A relay so you can use a smaller switch in the dash.
Note: This is illegal, I've never done it and I saw it on a show once. Don't do it.