...in Stand-Up Comedy's Golden Era, by William Knoedelseder. Just published, available in book stores and libraries near you. Game show related, and we can probably ask a certain producer more about this.
[David] Letterman's next break came courtesy of Tom Dreesen. A TV producer named Ron Greenberg recruited Dreesen to round up some young comics to help in auditioning potential hosts for the pilot of a new TV game show called Throw Me a Line. The comics would act as stand-ins for a Hollywood Squares-type panel of celebrity guests that was to include Zsa Zsa Gabor, Jack Cassidy, and Jan Murray. Their job was to throw funny lines back at the auditioning hosts, who included such daytime TV veterans as Jim Lange of Dating Game fame and Lloyd Thaxton. For the first half-hour run-through, the comics included Dreesen, Letterman, Jay Leno, Johnny Dark, and Elayne Boosler, who had just moved to town. They were paid $6 each, and all of them performed well except Letterman, who was so flat that Greenberg told Dreesen he didn't want him back for the second session the next day. "This guy doesn't get it. Find someone else," he said.
But Dreesen dug in for his friend. "No, no, I promise you he does get it, and he is very quick. He was just off today. He'll be great tomorrow. I guarantee it."
Outside the studio Dreesen found Letterman leaning against a parking meter, looking dejected. "I'm sorry," he said. "I was awful."
"Don't worry about it," Dreesen said. "Just knock 'me out tomorrow."
The next day Letterman tore the place up. The auditioning host was Lloyd Thaxton, who Dave addressed variously as Boyd and Floyd and even Hemorrhoid. When Thaxton read out one of the scripted questions, "Why would someone wear garlic around their neck?" David ad-libbed in a Hoosier accent, "Because it goes real good with a brown sport coat." Letterman was so sharp that he raised everybody else's game, and the session proved a riotous success (for everyone by Thaxton, who didn't get the gig). Jan Murray and Jack Cassidy had stopped in to watch, and Murray said to Greenberg, "These kids are wonderful. What do you need us old farts for? You should shoot the show with them."
In the end, the "kids" were paid $150 each and sent on their way. But Letterman had made an important impression. An NBC development executive named Madeline David sat in on the Thaxton session and came away convinced that the network should try to develop a TV show with him.