At the end of the "Don't Feed Phil" episode, Don Vito's toe nail is listed as a guest.
In the first season's scavanger hunt episode, the end credits list "The Sick-Ass Lake" as a guest star (a reference to the pond featured in one portion of the show).
In the episode where Raab marries his Russian mail order bride, and Phil and April renew their vows (Las Vegas), Don Vito's dent is listed as a special appearence.