Is `GOOGLE_VENDOR_NPM_DEPENDENCIES` supported for functions deploys?

Per the Google Cloud Functions documentation found [here](https://cloud.google.com/functions/1stgendocs/writing/specifying-dependencies-nodejs#build_your_function_with_vendored_dependencies), I was curious if this build variable was supported using the Firebase CLI? From a quick look at the source code it seems that it is not supported, so I assume that when using `npm` dependencies are always installed on deploy and cannot currently be vendored?