Based PURELY on conjecture, I would add hash or keif or whatever you are gonna use at bottling. It would be easier to consistently dose each bottle that way. Are you using priming sugar to carbonate your bottles? If so, I would add it then, after the priming sugar has been melted in a little water.
It is my opinion that the buds can be handled just like hops. For flavor and aroma I would add them to the kettle at the end of the boil, after the heat has been cut off and while you are cooling the wort. Then, for the THC addition I would add the buds in the secondary fermentor, just like you are dry-hopping. I'd leave them in there a week or so but that would be something you would just have to play with to get the exact time figured out. Most important would be to do this "dry-budding" after ALL fermentation is complete so as to keep all the flavor and aroma from being carried away by the carbon dioxide escaping during fermentation.
All stuff I've thought about in the past but back when I WAS homebrewing I never had the excess of bud needed to try this...
