Breathing compressed air at depth (I assume that is the case with your spare air container; Frankly, I am not familiar with the appliance). Be sure and keep an open airway and exhale continuously as the compressed air in your lungs expands; otherwise you are virtually DOA when you arrive topside.

The previous post gives good info on the problems with using a throw bag while in the water. I have used various kinds extensively in swift water rescue and I always had one aboard my kayak when pleasure paddling. They are a great tool when you have a solid stance.

Good for you in thinking about this difficult problem, but I am not sure your proposals are likely to be workable.
Geezer in Chief