I don't think that taking combinations of the mentioned compounds causes the body to metabolize one of them into a psycho-active phen.

It seems more plausible to me that potentiation of psycho-active phens by these chemicals is caused by the fact that the body would probably want to get rid of the most toxic substances first. So if you take mescaline and safrole toghether and safrole is the most toxic of the two and broken down by some of the same mechanisms, if the body then prefers to break down the safrole first because of it's higher toxicity, maybe a lot of mescaline is left untouched for a long time by all the bodily mechanisms involved in getting rid of it.

Something like this happens when you drink alcohol and eat something sweet or fatty. People who often do this grow fat, because the body wants to get rid of the alcohol so much that it put's less effort in getting rid of the fat. That's the reason some drinkers develop a beerbelly.