Remove "/site/XYZ/" from permalink on file upload

I desire a global default media path to be set for all current sites (and newly created). Sadly, I don't have a sub-directory network setup. I was thinking, I could even create a subdomain, and host the entire network images there. When image is upload on XYZ network site, it's uploaded to: http://media.domain.com/2015/05/downward-arrow.png

If you may, please point me into the right direction, I would be most appreciative.

Currently, when I upload a file this is the permalink:

http://domain.com/files/sites/27/2015/05/downward-arrow.png

How do I make it this:

http://domain.com/files/2015/05/downward-arrow.png

I have a subdirectoy WPMU configuration. I was able to Change Default Media Folder using your blog post - wicked helpful!