playstone

So, I will answer my own question!

It seems this is not possible.

So what I ended up doing is edit the /libs/class.package.php file to create my own shortcode and in there I do the condition to check if the file size is 0 and if true I include the HTML to generate a different button.

It was a simple edit, now I just need to remember to always update this file when the plugin gets updated.