Email seems like the right answer, but can you not put it in a sidebar, at the top of the page or probably best at the bottom of the content with a relevant CTA

Email seems like the right answer, but can you not put it in a sidebar, at the top of the page or probably best at the bottom of the content with a relevant CTA linking the article to your list? Unfortunately I'm guessing huge popups convert better, although I'm not convinced that's true if your audience are similar to this community.