Laravel 5: How do I change the directory of my custom config file from app/config to app/source?

I have a repository in folder app/source and a second project share the app/source with my current project. I need to move my app/config/config.php into app/source so my second project has the same data. How do I configure laravel to search for my custom config in app/source/config.php instead of app/config/config.php?
I've tried to update my ConfiserviceProvider class to this:

class ConfigServiceProvider extends ServiceProvider
{
/**
 * Bootstrap the application services.
 *
 * @return void
 */
public function boot()
{
    //
}

/**
 * Register the application services.
 *
 * @return void
 */
public function register()
{
    config([
        'app/source/config.php',
    ]);
}
}

but this isn't working.
How do I fix this?

via Chebli Mohamed