I must initially apologise for the terrible quality of the video and sound: my cameraman is away for the weekend, and I wanted to get this recorded to show it off, so I used my phone.
Anyway, here it is.
The effect itself requires a setup, but this is explained to the spectator: "every aspect of that packet is designed to influence your thoughts and actions." It's completely non-gimmicked, and can all take part in the spectator's hands.
(Another apology about the quality though, I understand it won't be the easiest thing to watch!)