I get the flakes and sprinkle it on top then very lightly stir it in to the top of the feed with my fingers. That way no one gets a bite of JUST the yeast.
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
Really good info on niacin in the link.
I am using nutritional yeast as it is higher in niacin than brewers yeast.