Can Elixir mix only the changed SASS files?

Lets say I want my Bootstrap or Foundation css to be a separate file along with my app.css.

If I make a mix for them and another for my app.scss, I get both my app.scss and the framework scss compiled every time I make a change to the app.scss.

This would be OK if it didn't take 5-8 seconds every time to recompile the framework scss.

Here is a simple code of what I have in mind:

elixir(function(mix) {

     var    bowerPath   = "../../../resources/assets/bower_components/",
            publicPath  = "public/";

    mix.sass('app.scss')
          .sass(
        bowerPath + 'foundation/scss/foundation.scss',
        publicPath + 'css/foundation.css'
        );
});

Is there any way to tell Elixir to compile only the changed files and not everything.