I should have been more explicit.
Qubes has the 'qvm-trim-template' available for the linux guest templates. I'm wanting to to same thing to a non-unix template.
That way I can truncate the file, or just shrink the space it takes up.
However, qvm-trim-template will not remedy the filesystem in a non unix template.
What is it I can do so that the VFS image takes up less space?