The celebrity cameos were not written in the script. Robert Altman added them all in. No scripted dialogue was given to any celebrity with a cameo.
According to a contemporary article in the New York Times, director Altman convinced the celebrities who provided cameos for the film to donate their union-scale salary for one day of work to the Motion Picture and Television Country House and Hospital for retired filmmakers.
The writer pitching The Graduate: Part II to Griffin Mill is a cameo by Buck Henry (as himself). Buck Henry co-wrote the screenplay for The Graduate (1967).
The handwriting on the ominous death threat letters and postcards received by Griffin Mill belonged to director Robert Altman, who took great pleasure in writing the notes.
Screenwriter Michael Tolkin had a film company ring him up and try to option Habeas Corpus, the blatantly ludicrous film that is pitched within the movie.
Joe Dallesandro: Star of many Andy Warhol films, appeared as himself in a restaurant scene cut from the final print.