Domain mapping leaves out domain alias and breaks images

We have a multisite setup using nginx. We map some blogs to custom domains but when this is done, the mapping changes wordpressmu.com/blogAlias/files/2014/07 to customdomain.com/files/2014/07 or with CDN it is CDNdomain.com/files/2014/07. This essentially breaks all the images. If I copy the image URL and add the ‘/blogalias/’ before ‘/files/’ that URL works but not sure how to redirect these correctly in nginx. How can we use domain mapping with nginx and have the images show up? We are also using nginx helper plugin and a CDN with W3 Total Cache, although images are broken with or without the CDN or nginx helper.

https://www.ads-software.com/plugins/wordpress-mu-domain-mapping/