Using a .yml (or other file) to dynamically assign config.php values

I got some experience in Symfony, and i am used to being able to fill in config values after the first composer install command, and since CI supports some Symfony modules, i guessed it would be possible here as well. Thing is, i can't call the Yaml library in the config file, and editing it after the file is loaded is hardly recommended. 

I imagine there must be some way to use a yml, json or xml file to externally load in configuration settings that have been defined in a composer install/update command. If there are any other ways that i can easily manage my project so that people can pull in the git and during installation go through the configs without having to edit the config files themselves, that would be nice.