yeah, i've done two wherries, and neither have "stuck" like some.
before I pitch the yeast I whip up the wort a good un until there is a good layer of froth on it. then I sprinkle ontop, and put the cover on the FV. i leave it there to rehydrate a bit and then I gently stir it in.
I sprinkle but I will admit I have latter stirred mainly having realized from the S.G. reading I must not have stirred enough to start with. Reading the on line guides it would seem yeast can double it's size every half hour so within a few hours it would not really matter what you did. However sitting on foam I would guess allows it to adjust to temperature slowly before re-hydration so likely less shock to yeast.
Stirring will allow more fermentables to come in contact with yeast so faster start but that is likely to equate to half and hour so does it really matter?
The faster the reaction the more heat and I am aware how easy it is to add yeast when a little too hot anyway. I now tend to start at 19[FONT="]ºC until everything has slowed down then ramp up to 20[/FONT][FONT="]ºC and I feel a slow start is likely a good thing.[/FONT]
I use Fermentis, and if you check their website it says hydrate the yeast in water at 27 to 30 degrees for at least 30 mins before pitching. I always do that, then stir in vigorously with a whisk for 5 minutes, always works a treat for me.