An enhancement to my enhancement idea:

Rather than defining a C.O. port as "Aux", since ESI is all into fixed features, why not make the Page Port a "fixed" Aux port, that supports DTMF and 2-way audio. It would basically be the same as a C.O. port, but it would be specifically for paging applications, would program into page groups the same way, and would allow you to have the C.O. Port page WITH your speakerphone page. I would consider that a pretty big advantage, if it were doable.