I'm not a historian, so I don't really know. But, naively, I'd try to find some historical evidence that the "slapping customs" you describe actually existed and were widely followed, and that someone actually took Jesus's advice and implemented it successfully. I would do so by looking through sources other than the Bible, such as works of fiction, historical documents, paintings and sculptures, etc. I could also try to tracing some oral folklore backwards through time, to see if it converges with the other sources.