Containerization pattern best practice question

I am dockerizing a Python webapp using the https://hub.docker.com/r/tiangolo/uwsgi-nginx image, which uses supervisor to control the uWSGI instance.

My app actually requires an additional supervisor-mediated process to run (LibreOffice headless), and I’m wondering what is the proper pattern to implement it.

The way I see it, I could extend the above image with the extra supervisor config for my needs (along with all the necessary OS-level install steps), but this would be in contradiction with the general principle of running the least amount of distinct processes in a given container. However, since my Python app is designed to talk with LibreOffice only locally, I’m not sure how I could achieve it with a more containerized approach. Thanks for any suggestion or help.