Elixir versioning with SCSS and JavaScript

How do I chain Elixir's .version() method with others? My gulpfile.js looks like this:

elixir(function(mix) {
    mix.sass("frontend/frontend.scss", "public/css/app.css")
       .sass("backend/backend.scss", "public/css/admin.css")
       .scripts(js, "public/js/app.js");
});

Do I just call .version() after this chain on my generated files? Like this:

elixir(function(mix) {
    mix.sass("frontend/frontend.scss", "public/css/app.css")
       .sass("backend/backend.scss", "public/css/admin.css")
       .scripts(js, "public/js/app.js")
       .version(["public/css/app.css", "public/css/admin.css", "public/js/app.js"]);
});

Or is there some way to combine .sass() and .scripts() methods with .version() to avoid repeating file names?

Another problem with my example is that it produces redundant unversioned files prior to creating versioned ones, so I have useless files there.

via Chebli Mohamed