I agree that if there is a monetary requirement it fails to be open source. That said, I appreciate the intention.
What about requiring a "powered by" type of mark that includes the organization that they support. Then you can let the organization audit that. They would know whether or not they received the $5.
That seems like a good idea, and is along the lines of things I've been thinking about to verify the donation. However if a business did not want to comply with the license they would probably just not include this "powered by" mark and we would be where we started.
Sure, and all sorts of systems are hacked one way or another. I suggest giving up on the idea of policing it and release that idea of control.
If your intention truly is social impact then focus on what can be accomplished by the participants. Forget about the bastards, they aren't worried about you.
What about requiring a "powered by" type of mark that includes the organization that they support. Then you can let the organization audit that. They would know whether or not they received the $5.