Thanks @kaiyes. Googling for UnCSS solutions, I’ve found this Meteor forums thread (which makes me feel dumb that I failed to find it while searching for similar forum threads before writing mine):
where the following hackpad is linked:
https://meteor.hackpad.com/Proposal-New-phases-for-the-build-process-KQ8jqchouGs
Unfortunately there was no conclusion if it’s possible at all.
Are there any news on that?