Use system environment variable in helm

I am trying to deploy an application using Helm, and I would like to be able to use a system environment variable in my helm chart.

I have a server with the following environment variable set:

server1 :~$ env
USER=build

In my values file, I would like to do something like this:

home:
  user: {{ env "USER" }}

So when I use values.home.user in my yaml files, it expands to "build" (or whatever is set as the system environment variable).

Is there a way to do this?