Fabric glue won't work because it might make the lace stiff and it can change the color of the fabric under the lace. And as you said it won't hold up to repeated washings and wearings. Sewing is actually far less obvious. Use a thread that matches the lace. When the thread is on top of the lace holding it down it won't show up and on the underside of the shorts where it's a different color it simply won't be seen. Use small stitches on the lace and try to have the sewing thread go the same direction as the threads of the lace. That will help the sewing blend in with the lace and be almost invisible. If you use a thread that's a different color or use long stitches that go in a different direction than the threads of the lace then the sewing will be obvious -so small stitches, same direction, and thread needs to match the lace.