Nope. There hasn't been one instance. Not one after 20 frickin' years. I suppose that if you were the executive producer of either one of these shows, and you were producing 52 weeks of episodes every year, your primary concern would be to make sure that "Stage Fright" would never, ever occur on your show. The only way you could to that would be to turn to a staffing / acting agency in Hollywood whose sole purpose is to supply professional actors and actresses to these various types of shows who play the various "Trailer Park Trash" guests on these shows.
Time is money, isn't it? And if you're the executive producer of one of these shows on a rigid and tight shooting schedule which yields one episode per day, you certainly couldn't have "real guests" from rural America screwing up your shooting schedule with chronic examples of "Stage Fright." So you would quite logically turn to this agency in Hollywood to supply you with seasoned acting pros on a daily basis to play the roles of "real guests" from "rural America."
And I gotta tell ya'!!" These professional actors and actresses are real professionals while playing the roles of these guests. Crying on cue just as Camera #3 locks in on them for a close-up. Shouting at and shoving one another while apparently oblivious to all of the various mini-cams on boom arms doing high speed aerial zoom-ins on their faces during the arguments.
It could be argued that all of these apparent "real guests" on these talk shows receive a high speed crash course in how to be melodramatic and theatrical in front of high tech cameras hours before filming begins....but I doubt it. I would even go so far as to say that there is a professional and accredited acting school in California that specializes in teaching professional actors and actresses how to play the roles of "talk show guests" from "rural America." Once they graduate from this school, they are immediately sent over to this staffing / acting agency in Hollywood where they are sent out to "The Maury Povich Show, "The Steve Wilkos Show", and "The Jerry Springer Show."