Looks like we’re going to be co-authors! I was working on this at the same time you were, apparently! 
- feat: make externalScripts configurable via env.config.js by arbrandes · Pull Request #876 · openedx/frontend-platform · GitHub
- feat: add EXTERNAL_SCRIPTS hook for configuring MFE external scripts by arbrandes · Pull Request #290 · overhangio/tutor-mfe · GitHub
Not sure what the best way to reconcile the two is going to be, but given mine are a tad more comprehensive in the code (tests, docs), yours more comprehensive in the test instructions, how about we start with mine as a basis? Care to review and test them? Feel free to shoot holes in anything you see that doesn’t look good.
(Out of curiosity, I also just put out an implementation of this in frontend-base land.)