The link on Premier is about two thirds down this page: http://www.premiereradio.com/category/view/prep_and_research.html
I don't see any problem at all with "seeding" a few callers to help make a program lively, interesting and entertaining. This is merely a manufactured "issue".
The mission of Premiere is not ideological but is to reach as many ears as possible in a desirable demographic to acquaint listeners with the products and services offered by advertisers.
"We're not in the business of providing news and information. We're not in the business of providing well-researched music. We're simply in the business of selling our customers products."
That brutally honest statement from Lowry Mays, founder of Clear Channel Communications (which owns Premiere, the syndicator of Rush Limbaugh, Glenn Beck and Sean Hannity) aptly summarizes the purpose of broadcasting and cablecasting in a consumer-driven, free market system. It's been that way since the first commercial aired on radio in the 1920's.
I well recall Rush Limbaugh in his days as a very good, polished top 40 disk jockey known as Jeff Christie. Then and today, he knows how to attract and hold an audience. And that is what makes advertisers happy and produces profits for Premiere.