Setting up the CO as a public speaker and assigning him a "congregation" seems like a workaround for what should be an independent feature.
And yet the functionality already exists. When creating an exception I can manually add the midweek and weekend final talk titles, and the CO's name is automatically assigned. It would be nice if it worked in the same way for the CO's (second) public talk. A CO's PT theme is most often a one-time delivery. Adding it to the list of public talk themes is thus counterintuitive.
A cleaner workaround for those using custom templates is to make use of the Public Meeting Notes field. Here is the code for it: