This is not an ideal setup. What would be better is to add some faircamp features and templates to jekyll and/or add more jekyll sorts of features like arbitrary pages and blogging to faircamp. Preferrably both so that people can have options. I'd be willing to assist with either as I'm familiar with both ruby and rust. I also have a separate music social media thing I'm working on. Anyway, I digress! Here is the basic, crude way I made jekyll and faircamp sorta work together so that I can have extra pages but use faircamp's generated output as the main template in jekyll for other pages.
Firstly, faircamp's output uses relative paths. That's a simple, logical way to make the generated output