Howard Stern's radio show is (still) the #1 morning radio program in most markets, including March 2nd states such as New York and California. Both John Edwards and Howard Dean should appear on the show to talk with Stern, particularly now that he's fighting censorship and he's opposed to the reelection of George W. Bush.
John Edwards has nothing to lose as the underdog. He needs to take risks. Stern isn't much of a risk, really. An appearance Monday could help push Edwards up in New York and California, particularly.
Howard Dean is perhaps a better fit for the program. (Stern can pull out his "scream" tapes, and the two can laugh about them. Dean can also give medical advice on how not to catch a sexually transmitted disease. That's one way Stern mocks FCC rules about what can and cannot go out over the airwaves.) Many of Stern's listeners are likely disaffected, and others are loosely attached Republicans. Dean, like Edwards, can help cement those voters at a critical time.
Unfortunately I don't think John Kerry will appear because his advisors would consider it too risky. But he should. Still, even without Kerry, Edwards and Dean both have good reasons to appear.