How to exclude files or trees fro being minified in an ember-cli project?

I have an ember-cli application that has dependencies to libraries that ship with both minified and non minified versions. The build-time is HUGE because of the minification process for those external libraries.

I'd like to use the minified-by-vendor versions in production mode. I know how to opt-in to use those files in production mode. The problem is that these files would be still minified, although they are already. So how is it possible to tell the buildprocess to not minify certain files or trees?