You would simply include the CSS language to your bundle via an "include" command, so keeping things up-to-date should be automatic in this case.
Ideally this would work, but unfortunately with the change I need to make to the language grammar it won't. I found a post on the list where Alan says he wants to make it possible to inject an include into the grammar from outside of it by using a scope selector, but that this will be a post 2.0 feature. So for now, doing what I want requires editing or copying the grammar itself.
Matthew