Definately if you contract the diaphragm, you are not going to assist! I think you mistook my meaning. I have heard of it referenced as a diaphramatic maneuver in the past, being the reason I stated that. Maybe that is not the best reference. Just as when you forcefully exhale, you are using muscles to squeeze the lungs meanwhile releasing other muscles. I stated you must have control (ability to relax appropriate muscles, while tensing others) over muscles in the vicinity of the thorax. I think it would definately assist to have control over various muscles in the thorax, don't you? Or were you just refering to contracting the diaphragm?
I as well stated in my post that such a maneuver is dangerous to the tissues. I don't recommend this at all. I was just stating the techniques that are possible and have heard of this being employed.
What do you mean by you 'plunge' the soft palate? 60m hands-free... nice! I will definately give it a try soon. What do you find with controlling the flow of air to the tubes, without seepage through the mask skirt?