Simply holding the vic upside down and still generates 1g forcing the obstruction away from the airway. That most first aid manuals mention alternative treatments suggests that this force is insufficient to reliable alleviate a choke. Studies on fighter pilots suggest that 2-3gs forces a life-threatening amount of blood pressure to the head unless relieved within a few seconds. G-forces in other directions are much safer, unless for some reason you need to be conscious or in control of your extremities, so if you want to kill someone on a centrifuge, remember to strap him in head outward. I'm not going to bother working out how much force is required to dislodge a grape from a trachea, but this proposal has an uncomfortably thin therapeutic margin.