Are you seriously proposing that motorcyclists get in FRONT of drivers on the highway with a sign on their back to provoke the drivers into going faster, for a micropayment?
No. If you read the comment you'll see that I'm not proposing that the slow drivers speed up -- but just that they get out of the passing lane. In fact, to your point about motorcycle safety, I'd encourage them to maintain their slow speed if that's where their comfortable, but just move to the right (when it's safe).