Hosting downloads on CDN won't allow users to download the product

I'm helping a client with a site and they have video downloads that people can purchase. Because the files are so large they would like to use a CDN (MetaCDN) to deliver their files, but when we add the CDN link that pull from their origin to the product profile the user is unable to download the file. Instead the get a 500 Internal Server error.

Is MarketPress trying to download the file and then serve it? If so, it there a way we can just redirect and serve it directly from the CDN keeping the masking URL intact?