1.)unplug the defrost switch>find a wire that only comes on when you have the key on>wire a relay to that switch using power from the battery> set up a couple more relays depending on how many outlets you want to convert>find the power wire going into the outlets you want to convert>splice power wires from said relays into power wires from said outlet.
2.)enjoy your new switched cigarette lighter outlets
3.)???
4.)profit