Writing a 12 Factor Application Using Webpack?

Question

How would you write an application with 12 factor webpack / expressjs? In particular, I would like to have some application configuration delivered at runtime using environment variables on the expressjs server.

I am currently creating a global Config object in tags <script>and populating it by rendering the template and passing values, but I would like to use external webpack resources and wrap this as a proper module. Has anyone tried to do this or had a similar solution?