How do I add another build task for specific files in ionic build scripts?

For UWP apps, a background task must be it’s own JavaScript file. The challenge I’m having is I need to run npm run ionic:build --backgroundupdater.task.ts on a separate file (and any dependencies it may have) into a single file.

I’m looking into a customizing ionic-app-scripts to do this, but have no idea what’s the best way to do this, or where to start.