I didn't know if you were looking for a video of the trick or the explanation. The trick can be found in The Art of Astonishment Book 3 by Paul Harris. Great trick!
Wack Your Pack requires a really strong personality to pull off. It can also be found in Mike Ammar's Magical Arts Journal Paul Harris issue. Another option for you is Vernon's Fingerprint Trick, which is very similar.
Yep, it's in book 3, but I personally prefer Juke. It's the following effect after Whack Your Pack. It's a tad larger of a routine, but still revolves around the same idea. It's a great card routine.