$ ng eject

This will generate webpack.config.js in the root folder of your project, and you're free to configure it the way you want. The downside of this is that build/start scripts in your package.json will be replaced with the new commands and instead of

$ ng serve

you would have to do something like

$ npm run build & npm run start

This method should work in all the recent versions of angular-cli (I personally tried a few, with the oldest being 1.0.0-beta.21, and the latest 1.0.0-beta.32.3)