Wasn't Larroquette already ON this show in some other role?
Or am I confusing it with "The Practice" (which is a linked show so it should still count...)?
EDIT: Yes, he was apparently on The Practice as a character named "Joey Heric". Which with that reminder I now remember the multiple episode arc with him in it.
EDIT 2: Lookee! "The Practice" The Return of Joey Heric (2002)
EDIT3: In fact... he won an Emmy for his role on "The Practice". John Larroquette - Awards