I don’t know that any subjective experience can be ‘demonstrated to “materialists”’, as you put it, but that does not mean that those experiences do not exist for the folks that had them.
Every so often I play with the notion that the experiences that I am evaluating are not as I presume they are; that they are the products of the subconscious, say, or similarly unique to the inside of my head. With that as the presumption, I judge whether or not the tools of my religion are useful, and find that they still accomplish the effects that I am looking for.
Coming up with something that can be ‘demonstrated to “materialists”’ isn’t terribly interesting to me. I have a toolset that works for what I want to do, and I test its efficacy somewhat regularly; I can see no way in which one can justify that this is in any way equivalent to “the world is not real”. I am satisfied with my tools; the fact that other people do not find my tools satisfying is very nice for them, I’m sure. I see no more reason that they should care about the contents of my toolbox than I care about theirs.