Wow. The internet is an amazing thing.
University of Nebraska - Lincoln has posted Carson's 1949 senior thesis "How to Write Comedy for Radio" - a reel-to-reel recording wherein the young Johnny dissects the structure of radio comedy. This was mentioned on the PBS television comedians special recently...
It's a large file (69 megabytes) but well worth listening. Clips from Jack's show are abundantly used to illustrate his points. This would be an awesome discussion topic for a chat some month.
Here's the link:
http://digitalcommons.unl.edu/theaterstudent/1/