It's possible to use environment variables at the API definition?

On a multi-environment, dev and prod for example, it’s possible to reuse the API definition files? I would like to do something like this:

  "proxy": {
    "listen_path": "/v1/users",
    "target_url": "$USER_SERVICE",
    "strip_listen_path": true
  }

Most of our services have the same configuration, the really only difference is the actual service endpoint.