You could try a valance made of fabric with some padding inside to give it weight similar to this one in my LR which with the corner piece is almost exactly the same length as yours . I ran a 2 x2 on the wall added velcro to that with a staple gun and then sewed the valance added the other part of the velcro to the fabric and just stuck them together the nice thing is it comes off if it needs washing and weighs ery little . I used my same drapery fabric with some polyfiller and just a simple line of stitching every 6 “ took about 6 hrs all together most of that time cutting and pinning