Include js files outside static directory in node.js

i'm building a platform which has a folder called "extensions" in which are stored some plugins activable for the user (the activation is based upon a db table that records the userid and the plugin he bought). For each extension, the file structure has a folder called "js" in which i store the jquery valid for the views of the extensions. My problem is : how can i include the js script of those extensions even if they are not in the express static directory?

via Ermanno Palmizio Salieri