Not so much a visual flourish as a conceptual one: the Pittsburgh Public Theatre production of "The Fantasticks" last year set the show even more explicitly as a play within a play, and built a miniature theatre and rehearsal space into their space. The show was then presented as an "observed rehearsal:" El Gallo/Narrator was the play's director, and the Mute was his stage manager, perpetually and silently cueing effects, moving elements in and out of the playing location.
The two moments which stick out to me from that were the very opening, in which the stage manager/Mute enters the space and gave a silent, stone-faced "curtain speech," indicating the exits, turning off phones, etc. before taking his seat at the producton table and cueing the band.
More complex was the El Gallo role: the Director, a man of no determinate or implied sexuality, was playing the role of El Gallo in his own play. El Gallo was implied to be a gay man (hints of "male gigolo" even), who then played the role of the very heterosexual "El Gallo the bandit lover" to manipulate the young lovers. It was a master class in subtlety watching the transitions of layers and role-playing, as the "bandit" faded back into being the "gigolo," who would then step out of the storyline and address the audience as the "director." No funny accents or caricature was involved- just a very careful, nuanced portrayal of a character who plays a character.