I think glue is suitable for basting if you are going to wash the quilt afterwards, when the glue comes out. Even if there are globs of glue and puckering, it really doesn't matter if the quilt is washed.
For a wallhanging that won't be washed, I think it would be a much better idea to spray baste with 505.
Since the wallhanging already has the glue in it, the suggestion to soak it in water to dissolve the glue is going to be your only solution to the problem.