Rewrite root/uri path within CSS

[IngwiePhoenix]

I am using the extract plugin in conjunction with one or two self-made loaders that turn code into plain CSS. Now I just figured out that some - if not, most - of my image resources are using root paths. For instance:

#bg {
    background-image: url("/cdn/images/bg.jpg");
}

Now I want to re-write these paths automatically, so that they are processed by image optimizers, for example.

What would be also nice is to re-write the @import statement's URL that has an URL to the font used within Bootstrap. Since I use Bower to install Bootstrap, i can't quite change that bit away...so I need a way to get it either changed to a local path or get it removed/stripped.

Any help on this one?