As I said, a chum in highschool told me about it, mentioning only that it was one of the Droll Tales. The king was a bit of a sadist. Etiquette very positively barred the attending nobles from leaving until the King gave them permission to do so, fully intending that all should have soiled themselves before they could get home.
Actually, I think that croton oil, even in the very small effective dose, would be very readily detected, and the wine would be dumped into the potted petunias, if there were any handy. One of the substances found in the oil is
valeric acid, which is one of the things that makes garbage smell so bad.
I spent hours trying to see if I could find the story, but no luck. Sob,sob!