Prepending CDN url to all image references in grunt task

Question

I use a default grunt build, which replaces all image references with name+hash in the source code. This was when I had all the images in same place as my index.html

Now I need to use CDN to store images. I used grunt-aws-s3 for uploading all images in my /images folder to CDN.

But how do I prepend all the image name references with my CDN URL?