Not to sure really, sounds plausable. However theres a lag phase before the yeast start to acctually ferment the beer when it takes up nutrients, which, according to my 'yeast book' can be anything from about 4hrs to 15rs. During this lag time I don't think the yeast are making a protective layer of C02. By the time the yeast are make C02 the foam on top of your wort from aeration will have subsided and the yeast will have made it into the main body of the wort and probably sunk to the bottom of the FV by now. So I don't think sprinkling on top to try to make this protective layer sooner matters anyway
Also even if the yeast are making C02 at the bottom of the FV rather than when it's floating on the foam at the top wouldn't it just rise through wort and create a protective blanket anyway? Overall I'm not really that sure.
For me this shall I stir or sprinkle is moot anyway because you should really rehydrate your yeast as not doing so kills u to 50% of it because putting yeast in 20C wort is too cold for it and ruptures the cells (again according to 'the yeast book'). These dead cells have the potential to cause off flavours in your beer
