The problem is that biblical Christianity requires no (not one) ritual (Romans ch. 14; Col. ch. 2; etc.) The TRUE God seeks those who will worship Him in spirit and in truth (John 4:24), not in earthly ritual, earthly washings, earthly temples, earthly shrines or earthly priesthoods.
But(!) I wonder if we could come up with a few rituals (just for the fun of it) that we could say require some modifications of public facilities. I would do it for fun, but I’m afraid somebody would actually create a new religion out of it.
It would not require any public money for a Nativity Scene.