Testing to require system gems from within a bundle even though they have been excluded from bundle install

Gemfile

source :gemcutter
group :gems do
  gem "haml", "~>2.2.0"
end

session

(haml lib installed on the system)

$ bundle install --without gems
Using bundler (1.0.0) 
Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed.

/usr/src/test_bundler_without_gems
$ ruby ./test_bundler_without.rb
<p>Haml code!</p>
:)

test_bundler_without.rb

require "rubygems"
require 'bundler/setup'

# require your gems as usual
require 'haml'

engine = Haml::Engine.new("%p Haml code!")
puts engine.render