Hi,
the latest version of the app support fixed URLs in the config.json but it requires gulp to work, in any case, what you can do is use our custom code for the Learn Moodle app:
See:
https://github.com/moodlehq/moodlemobile-phonegapbuild/blob/learn-moodle/build/mm.bundle.js
and replace there the learn.moodle.net URL with your URL
Juan