I used to do this to my girls' jeans after school let out. Great way to boost the summer wardrobe for next to nothing! Transform an old pair of jeans into adorable summer shorts using bias tape. Instructions on the site.
Save your too-tight favorite pair of jeans or slacks with these inserts. You also get the look of tailored pants but the comfort of elastic-waist pants. Step-by-step illustrated instructions show how to stitch into finished slacks or alter a favor.