D-Bag from MOTOR TANDEM how to rig????

Want to D bag from motor tandem paraglider. Launching requires that passenger is at normal connection point hight, we are launching from a flat road. Would like to have the D bag below pilots feet at time of deployment and weighting of passenger at glider connection points so that, so the pilot doesn't drop and bag goes over pilots head. Our idea is to lower pilot and D bag into deployment position in flight. Ideally the top of the bag is under the pilots feet. Having not done this before, looking for suggestions or knowledge as to the way its done. Climbing harness, Dynema runners and Rope and GriGri for lowering seems complex, doable but complex. Looking for that beautifully simple, clean solution.