Steps involved to use Ionic 2 as progressive web app in non-ionic webpack build

I would like to add an Ionic 2 progressive web app (ie. non-native just standard ng2 app) to our existing set of Angular 2 applications managed by our webpack build. Is there a set of instructions for how to build an Ionic app outside of the ionic cli?

More specifically, I would like to get ionic building inside a build for multiple web applications that is based on The main things I am trying to solve are issue like how to create the base scss file that imports everything, what assets are needed, etc. I can get the ng2 application side working but it is the other parts around it where I can’t find any examples.