You reason with a religious person just like you would with any other person. If they don't want to use reason, their loss. If they cannot come up with good reasons for why they believe the things that they do, either their method is deficient or their faith is. Saint Aquinas' Summa Theologica does not consist entirely of threats and cajoling, and St Augustine did not defend the Church by refusing to engage in debate.
And it is also illogical to claim that a theists arguments are not worth listening to because they're the equivalent of treatises on Fairies, Unicorns etc,so it's good to see that you consider a rational debate something to engage in. Truth matters, and if you really respect someone you wouldn't let them hold a deficient view of reality.