Just to know, this isn't a particularly uncommon problem. I spent quite a few years working in the B2B lead generation space, and there are countless companies built around the value proposition of being a complementary product to another software platforms.
There are quite a few techniques you can use to suss out what software and platforms companies are using internally, in order to better target your prospecting. Or you can skip that step and go straight to purchasing a list of companies that are known users of that platform. There are companies that curate that type of information - similar to BuiltWith or Wappalyzer, but include internal-only technology and not just what's visible by crawling their website. Or you can take it even further, and commission a custom program from a B2B lead generation firm which includes a requirement that any leads have self-reported that they use a specific platform and that they have decision making authority over it. There are also a ton of options in between; feel free to reach out if you'd like to chat more (email in profile).
 These are a patently different class of lead generation program than what the article references - both in quality and cost. You're looking at $20-$50 per lead vs. $1 per lead. But with a guarantee that they match your targeting and pre-qualification criteria, even if that pre-qualification criteria was as random as "she has confirmed they use Khan Academy internally, and that she's in charge of it, and that <insert your complementary product's niche> is a pain point for them".