You can also use a lightweight non-fusible interfacing as an overlay. Just make sure that you can see through it. Trace your pattern onto it, then use a long running stitch (or a machine basting stitch) to sew it on the top edge of your background fabric. You then roll it up and pin it when you are sewing your pieces down. A lot less expensive than clear vinyl, and you can either use a Frixion pen to trace, then press to remove the markings so you can use it again for the next block, or a fine point Sharpie and keep the overlay with your pattern, in case you ever decide to use it again. Karen Kay Buckley sells a product that she used when she taught the machine applique class I took at the Houston Quilt Festival last year. Just check out her store on her website store.