The general thing done for making the soil more acid in one place is peat moss and cypress mulch. Of
course, it would
be nice to find stuff free and more local.
Oak leaves and pine needles are suppose to decompose to acidic soils, but i have also heard that this is a myth, they like to grow in acidic soil but they dont make it, I honestly do not know so i figure it cant hurt to toss some under the rhotodendrum bush (however that is spelled). I suspect that they help, hey organic matter never hurts, but both break down slowly. I think coffee, something i never hear of, is a wonderful idea...the coffee in my cup is acidic why not the grounds and chafe (i roast my own).
Although there is some products which will immediately change the ph of your soil lower (i know all this since my soil is more basic than yours
) garden sulfer sounds more natural and gentle to me. I am not big into running to the store and buying what they have to make changes but i would do this to save the bush (if it needs saving).
Whatever you choose, a thick layer of one of the acid making mulches each year will constantly renew the acid around it.
If the bush is young and has not totally covered its eventual drip line, I think I would....well i love peat moss....i would dig out a few inches of soil away from its
roots and add peatmoss and work it in a bit (hey worms will come and mix it around more right?).
grey water, i dont know if i would use it on the blueberry or not but if i found it necessary i think i would make it go through my acid things otw to the plant.