feature request: disable prepend for some files, but keep fingerprinting

Hello, my use case is the following: using web workers with Ember:

```
this.worker=new Worker("assets/workers/worker_ls_serializer.js")
```

For the files in my workers folder that I call with `importScripts`, I have to disable prepending the CDN because of CORS issues for worker scripts (has to be the same domain), so I'm using `exclude: ['worker']` though we need to still keep the fingerprinting for normal version control.

for reference: https://github.com/ember-cli/ember-cli/issues/1011 http://stackoverflow.com/questions/24175120/ember-cli-project-and-web-workers/36529757#36529757
Thanks,

L