Josh joined a host of other celebrities including Jake Gyllenhaal, Jimmy Fallon, Joanne Woodward, Paul Simon & Elvis Costello a benefit for Paul Newman's Association of Hole in the Wall Camps at Avery Fisher Hall, Lincoln Center . New York City on April 2nd.
Josh sang "Changing Colors" and "Smile"...
(Image Source - 1, 2 & 3)
Here's a video of the stars arriving and leaving Avery Fisher Hall. Josh is seen very briefly at 1:14
You can also see Josh's performance of Changing Colors which is part of the EPK here.
In this video from the red carpet, Josh talks about being in the Tenacious D "To Be the Best" clip.