Cut a piece of 1 / 2 inch elastic long enough to fit around the waist of the person plus another three or four inches. Mark the actual waist measurement on the elastic with a sharpie so you will know where to sew when you're ready. Hook one end of the elastic to a big safety pin and thread it through the waistband taking care not to twist it as you go around. Bunch the pants up once you get both ends out, overlap the elastic to the sharpie mark and sew the elastic together using a wide zig-zag stitch for security. Trim off the extra elastic and let the elastic go back up into the waistband. Then sew across the opening to secure it all inside.