Image Path for MaxCDN for Multisite

We have removed the image base url for many of our images on our multisite.

Instead of using:
http://subdomain.multisite.com/files/year/month/image-name.png
we just used:
/files/2013/07/how-it-works.png.

This still shows the images but when we enable the CDN, the images are not added to the CDN and they 404.

Do we need to go back through our sites and fix the image paths to include the base subdomain path or is there a rewrite that we can use for force the site to look to our local server instead of CDN in case of a 404?

http://wordpress.org/plugins/w3-total-cache/