Force download of asset file from template
I don't think you're going to be able to do this out-of-the-box, but should be stupidly simple with a quick plugin that registers its own Twig extension.  See here for an example.

That extension would add a Twig function that's basically just a simple wrapper for PHP's file_get_contents.

Then from your template, you'd do something like:

{# Get the file contents #}
{% set contents = file('/path/to/asset.zip') %}

{# output it #}
{{ contents }}