Yup. Really any piece of metal that is close would do. Part of an old fender, or just about anything can serve as a patch as long as the metals are the same for welding. I use this for the copper backing when I can:
http://www.harborfreight.com/welding-spoon-66785.htmlAny piece of copper will do. Of course, if you don't have a piece of copper, just hold the piece to the hole with vise grips or something, tack it in place, then finish.
