How do I exclude assets from being copied to dist with Ember-cli?

There does not seem to be anything in the documentation about this (it only mentions how to exclude files from fingerprinting).

I have an entrypoint (app.css), which imports all my css partials with rework-npm. That works fine, but ember treats the css partials as assets that should be copied to dist/, since they have a .css extension.

Does ember have a way to exclude files from being copied to dist/assets?