This article has a good list of those who've performed recently for the USO
http://www.usatoday.com/news/world/i...so-cover_x.htm
Comedians for the USO - real-world
There is a real-world group called "Comics on Duty"
Stephen Colbert has recorded his show to a USO audience
Al Franken
Robin Williams
Drew Carey
Other (foreign) candidates that might work in the canon period
Rick Mercer (Canadian. well-known for supporting Canadian troops)
http://www.thestar.com/entertainment/article/174660
Billy Connolly (British & proud veteran of the Territorial Army)