Quite a few years ago I stopped in a gas station during the winter and this guy had a 50 gallon drum that he would fill with waste oil from cars. He had a hot plate under the valve on the drum that he would crack open and it dripped on the hot plate. It heated the whole garage. Seeing as you are already thinking outside the box, may be a smaller waster oil heater can be made for your stove top that would use your vent over the stove so you won't have to put another hole in the roof, a fireproof back splash could be constructed against the back and side walls for safety. Keep us informed of you progress.