I haven't read the source for the linked library yet, but could you just have javascript in your pages that hits a /gen204 page on your site when the DOM is rea

I haven't read the source for the linked library yet, but could you just have javascript in your pages that hits a /gen204 page on your site when the DOM is ready ? Then the preloaded page will only hit the /gen204 if it's actually rendered. Then just count the 204s instead of 200s.