4 is the bare minimum if you want to still have rudder control. The easiest way would be to cut a slot for a servo in the very center of the wing at the top. Then you could cut out the ailerons on the wing's trailing edge to whatever size you want (the bigger, the more stress on the airframe but the faster the roll rate) and add some dubro control horns or something similar along with hings and pushrods and you'll be good to go.