ET has uploaded a short video clip revealing an early sneak peek at the cast of “Glee” Simpsonized! Three “Glee” cast members — Lea Michele, Cory Monteith and Amber Riley — will lend their voices on an upcoming “Glee” theme “Simpsons” episode that will air September 26, 2010. Check out the preview clip below and let us know what you think. Has “The Simpsons” jumped the shark yet?