"So without anyone being able to see into the future, including me, Gay can indeed claim that
A. He doped unknowingly
B. Drummond encouraged/facilitated it.
since in retrospect, he realizes the significance of Drummond carrying the stuff and encouraging him to use it."
You assume that he realizes the significance "in retrospect".
Given his knowledge of WHO Drummond is, and that he was doped as early as 98 according to Laynes, it is not credible that Gay's realization was made only "in retrospect", but "in prospect" instead.
He absolutely knew what he was doing, this was the plan, that Drummond would be the one to take the fall, and Gay would have plausible deniability.
It might have worked, but for Gay's foreknowledge of Drummond's character.
It's not even a nice try. If I were prosecuting this, they would be squirming, a lot.