Another trick for an unassisted take-off, often practiced by pilots behind the Iron Curtain when towing back from a real field landing: use a really short towing cable (15 meters or less). When the towplane revs up with brakes on, there should be enough wind generated by the propeller to lift the wing at 0 kts. Jou need to take into account the side the slipstream will be going (propeller rotation + crosswind). But you need training to tow with such a short cable.