I agree with the "cannabinoid receptors have to be awakened" theory, but there are two options that I believe may increase the risk of getting high the first time consuming cannabis.

1.) Eat it, don't smoke it
2.) If you do smoke it, smoke A LOT. Just have them take as many rips as possible until they're lungs are burning up to an almost unbearable degree. That, I think, would get just about anyone high their first try.