Dynamic partials possible?

[pykong]

Can we get the file name of a partial from a variable?
This would be useful for customizing pandoc template, e.g. we would be able to refer to different
partial files in the pandoc frontmatter to be included in the template.

Conceptual example:

${ $partial-file-name$() }

I can not get it to work with the current incarnation of doctemplates.
This might be by design.