How can I manage an Addon's config if there is no structure?

I’m developing a simple add-on to run a third-party app. It’s a Dotnet application and has a json file with a bunch of settings.
There are far too many potential settings that might go in this file for me to justify the development of a bashio template, so I want to have a single config entry that has the default collection of settings in it; and for this collection to end up - as is - in the applications settings.json file.

Unfortunately, I don’t know how to do this, and I can’t find any documentation that might guide me.