Originally Posted by
cjsews
Is it possible to sew a strip of batting to the seam allowance after swing the binding on? Stitch alongside the seam. Maybe use a long zigzag stitch if you think it needs a bit extra to hold it. I would put a little wider strip on for ease of handling and then trim it down where you want it to be
Because it is just filling the binding, I would use light weight iron on fusible interfacing to attach a wider strip as ccjsews said, and then re-trim.