I wonder what would happen if you put it in the washer with a bunch of color catchers. You're still going to have to get it off of the white one way or the other; whether you keep it in the quilt or not. I would be reluctant to just remove the blue and continue to let it sit there on that white. You say you already pre-washed it?
That's the major thing I don't like about Batiks. I will wash them over and over until the water is clear. Sometimes I end up with faded fabric. But It's not too much to avoid that bleeding. Aren't you glad it happened to you instead of the recipient?