Others looking for a solution. With help from Bastian, this is how you can achieve what I was looking to do:
"Let’s say this is your setup
example.otf
example.otf.txt
example.oft.png
In example.otf.txt you could set the template:
Template: font
Then add a blueprint:
site/blueprint/files/font.yaml
And in there set the image options like this:
title: Font File
image:
query: file.siblings.findBy("name", file.filename)
This should work in theory. "
And works for me!