That could work, yeah. The effects of another magical plant in the book lasts for several hours after being cooked and eaten, so there's no reason the effects of the truth flower (I forget the technical name in the book) couldn't also last all day in the right circumstances.

Maybe Liir tries it in a kitchen experiment and Things Go Badly? *shamelessly volunteers someone else's character, yep!*

ALSO in the book the person who had been telling the truth forgets the conversation as soon as she steps away from the flower, so it has that cloudy lack-of-consequences thing that Piper's spell had.