The problem is that it's so jarring to hear his magnificent singing voice arising from an animatronic monstrosity... especially since he doesn't do the character Tennessee's dialogue (Tennessee sounds like a hick when talking) but just the music.
This clip shows them very briefly, but sadly the dialogue at the end was cut out. :( You do get to hear Don sing as Tennessee.
[ame]http://www.youtube.com/watch?v=JhI7C1Ha_pk[/ame]