Read wp-config without loading the rest of WordPress – i.e. wp-settings, etc

Actually you can read all the constants defined in wp-config.php from any place you want. If you have something like this in your wp-config.php

define('DB_NAME', 'some_value');

You can do this for example in your functions.php file

echo DB_NAME;

Constants are globally accessible from everywhere.

So please think about this approach.