One thing that may be useful is simply to get believers to specify exactly what it is they believe.
They talk in very high-flown, metaphorical language - "your soul's eternal destination", etc.
It's a mixture of a spiritual practice and vague beliefs about reality.
So if you ask them to specify exactly what they mean by their vague language, it gets them to think more analytically about what exactly they believe.
That isn't at all argumentative, it doesn't have to be tiring, and it strips off the vagueness which can sneak weird reality claims in.