How would I include polyfills only in "nomodule" differential builds?

[JulianSchoenbaechler]

I want to include core-js polyfills only into a referenced nomodule script tag, when I have a HTML file as main source. I have something like the following package.json.

{
  "name": "my-project",
  "private": true,
  "version": "0.1.0",
  "source": [
    "public/index.html"
  ],
  "type": "module",
  "scripts": {
    "clean:output": "rimraf dist",
    "start": "parcel",
    "build": "npm run clean:output && parcel build --dist-dir dist --no-cache",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "dependencies": {
    "core-js": "~3.39.0"
  },
  "devDependencies": {
    "@parcel/packager-raw-url": "^2.13.3",
    "@parcel/packager-xml": "^2.13.3",
    "@parcel/transformer-sass": "^2.13.3",
    "@parcel/transformer-typescript-tsc": "^2.13.3",
    "@parcel/transformer-webmanifest": "^2.13.3",
    "@parcel/transformer-xml": "^2.13.3",
    "parcel": "^2.13.3",
    "rimraf": "^5.0.7",
    "sass": "^1.83.0"
  },
  "browserslist": "> 0.5%, since 2018, IE 11, not dead"
}

The index.html references a JS file like so

<script type="module" src="/src/index.js"></script>

This creates two JS outputs (type="module" and nomodule). So far so good. Now I'd like to have more control on what gets included into the legacy nomodule build. For example, I want to include some polyfills only into the nomodule parsed output. If I for example add

import 'core-js/stable/promise';

to the referenced index.js, the polyfills are transpiled into all outputted JS bundles.

As far as I can see there is no way to control the differential builds whatsoever. Am I correct in this assumption?

If so, the only way to create legacy bundles based on the nomodule attribute, is to declare separate targets for each source file and manually add the built scripts to a main HTML file...