Are the quilting stitches really small? That would make removal more difficult. Also, I am wondering what kind of batting it is. If it's Warm and Natural, which is needlepunched through scrim, the scrim may remain even if you get all of the cotton batting fibers out. (Scrim is a very thin, lightweight polyester fabric.) I do think water might help as it would soften up the fibers and maybe help them clump together. How about using a soft toothbrush once the fibers are wetted? Might be enough to help pull the batting out from under the stitches. Just be careful not to scrub too hard.