This is a really common problem with about every small or medium sized bike club I know. See the other thread rolling around about "group ride etiquette" question ( http://forums.teamestrogen.com/showthread.php?t=17872 ) .
Some clubs rotate the ride leader for the "everybody" ride, so that one person isn't always the one getting the slow ride. They have to be organized enough to think of that and do it, though
See if you can bring others into the fold. For a long time I could go 40 miles, but at 12 mph. - a function of skill and my bicycle. There's a big group of folks like that in the Richmond Area Bicycling Association (or at least there was) - only when I moved away did I discover that's uncommon. Even out here, our beginner ride on Saturday often goes 20-25 miles, though we do not have hills and that makes all the difference.