How to make promise-based config work with `electron-webpack dev`?

I've been using electron with react-scripts for awhile now, and I'm in the process of replacing react-scripts with electron-webpack. I'm trying to use the [extending as a library](https://webpack.electron.build/extending-as-a-library) documentation, which explains that a function returning a promise can be defined as the webpack config.

Unfortunately, this seems to depend on adding a direct `webpack` call to my scripts rather than calling `electron-webpack dev`. I don't see an explanation of how to make `electron-webpack dev` use my new webpack config though. How do I do that?