Added Jan 21, 2013
New York, New Yo...
Iron interfacing to wrong side of inserts. Pin strips to trousers, right sides facing. Turn under 4cm (1 5/8") on upper edges and 1cm (3/8") on lower edges. Sew in place.
Try trousers on. If the trousers are too large, pin away the excess fabric on the trousers, leaving the fabric strips equally wide from top to bottom. Then stitch the fabric strips in place and press seam allowances toward strips. Turn allowances on ends of each fabric strip to wrong side and stitch in place, at width of waistband on upper edge and even with hem stitching on lower edge.