Go ahead and see if your local auto supply house has a product I think is called "muffler bandage". Try it -- you have little to lose.
Another trick that may work is to get an old piece of muffler pipe, cut a half-round or something that fits over the hole, and patch it using a muffler clamp. Don't have an old piece of pipe?... the same store may have some small pieces for sale.
95 E320 Cabriolet, 131K