My thanks to both Alexajlex and DeeDoubleYou for your suggestions. Given the cost of buying a second wide converter lens, I'll stick with what I have already and hope that in the not-too-distant future either Canon or someone else will manufacture a filter and lens hood that can be used with the Canon wide converter.
I've done a little more research, however, which I'll offer for the benefit of anyone reading this and who is considering a wide converter lens for the S5. As DeeDoubleYou suggests, the Raynox lens appears to be a good choice. I say "appears" because I have no personal experience with this lens. It seems to be a quality product, and unlike Canon's wide converter for the S5, the Raynox lens is threaded for filters. A filter will protect the lens glass (very important!) but vignetting may be a problem, especially if you add a lens hood. The thinner the filter, the better.
If you have an S5 with the 58 mm lens mount, be sure you purchase a wide converter lens with a 58 mm screw mount. And of course, you will need the conversion lens adaptor sold separately, either Canon's LAH-DC20, or the equivalent from other sources. Lensmateonline lists the Raynox DCR 6600 PRO for about $140, but it appears they currently have it only in 52 mm thread mount. The Raynox web site (www.raynox.co.jp
) lists the SRW-6600-58LE with a 58 mm thread mount. It is the same 23 mm focal length equivalent for 35 mm film as the 6600 PRO. It doesn't appear that you can purchase Raynox products directly from their web site. However, the information about their products should help you find a source from which to purchase.