Build custom modules for server side rendering in Express js

I searched all over the site (and also the internet), and did not found anything. I am building a server side rendering web application using webpack, express js and react, and there are some modules/files that i do not want to expose in my minified bundle file (business rules, sync files, and so on...). My point is to, somehow, my application uses the modules that i want hidden, and these modules be acessible from my server.

Any ideas of how to do it?

via erickles