I write my Markdown files with a YAML header consisting only of metadata fields relating to the content, like title, author, etc.

In another file format.yaml I have the YAML metadata applying to the formatting, like documentclass, font- or papersize.

How can I inject format.yaml into pandoc, so that it is used when I convert my source to LaTeX? I'm looking for something like --include-in-header, but for YAML and injected before the template is set-up.

Many thanks for any pointers!