Add cache-buster to non-optimized bundle?

Why do you need to? In development, where BundleTable.EnableOptimizations = false nothing is cached anyways, and in production you should have BundleTable.EnableOptimizations = true also negating the need for something like this.

The short answer, is no, there's nothing built in to allow you to do what you ask, primarily because of the reasons I've already stated: there's simply no need for such a feature.