The 20 something lines of Compass that I need.

sprite.rb

require 'compass'
require 'tmpdir'

template = %Q{
@import "icons/*.png";
@include all-icons-sprites;
}

options = {
  :syntax        => :scss,
  :line_comments => false,
  :cache         => false,
  :force         => true,
  :load_paths    => [Compass::Frameworks[:compass].stylesheets_directory, Compass::SpriteImporter.new]
}

Compass.configuration do |config|
  config.sprite_load_path << Dir.pwd
  config.generated_images_path = Dir.pwd
  config.images_path = Dir.pwd

  config.on_sprite_saved do |filename|
    puts filename
  end
end

engine = Sass::Engine.new(template, options)

puts engine.render