This is a really cool concept, using SIRI's native features to find a forced song.
Great idea from Jeff Prace.
This article also made me think that you could eliminate the force altogether by using a multiple-outs variation. In fact, SIRI seems to have the potential to be the perfect mentalist's assistant, capable of giving different answers based on a secret code system.
You could do a classic 2-person mentalism act with just you and a cell phone. I think the possibilities he brought up are endless, and these would make a great series of follow-up articles.