A more effective route might be to complain to your local radio station that carries Rush Limbaugh's show.

Several years ago I emailed my local talk-radio station to complain about Dr. Laura Schlessinger. (I used to listen to her regularly in my car while I drove to work, although I usually disagreed with her and didn't like her.) I got a reply from the program manager. It was very brief, and I can't remember exactly what it said, but I got the impression it was not a "canned" response, but personally and individually written. He thanked me for my opinion and sort of implied that a lot of people were telling him the same thing. A few weeks later, they canceled her show. (I mean, her show continued to be produced and syndicated, but my local talk-radio station no longer carried it.) I can't remember what they replaced her with; it might have been something equally obnoxious, but I considered it a victory nonetheless.

Whatever you say, I think it's helpful to give the impression (I assume your ethics don't allow you to outright lie) that you generally like talk-radio and would be a regular listener if only they replaced Rush Limbaugh with something more decent and credible. It might be helpful to praise some other program that's carried by the same station—or, if you can't do that in good conscience—praise a show that's carried by some other station such as NPR. You definitely don't want to give the impression that you wouldn't listen to their station no matter what they do, because then they have no incentive to try to please you.