Bundler in Rails 2.

bundler_with_rails(2.3.5).rb

## config/boot.rb
# Place this snippet right above the "Rails.boot!" command at the bottom of the file.
class Rails::Boot
  def run
    load_initializer
    extend_environment
    Rails::Initializer.run(:set_load_path)
  end

  def extend_environment
    Rails::Initializer.class_eval do
      old_load = instance_method(:load_environment)
      define_method(:load_environment) do
        Bundler.require :default, Rails.env
        old_load.bind(self).call
      end
    end
  end
end

## config/preinitializer.rb
# Create this file and paste the code in
begin
  # Require the preresolved locked set of gems.
  require File.expand_path('../../.bundle/environment', __FILE__)
rescue LoadError
  # Fallback on doing the resolve at runtime.
  require "rubygems"
  require "bundler"
  Bundler.setup
end

## Install bundler
# cd /path/to/RAILS_ROOT
# gem install bundler
# bundle init

## Generates a Gemfile in the RAILS_ROOT
# Here's a simple template to start off with
# Default RubyGems Source
source :gemcutter

# Ruby on Rails Framework Requirements
gem "rails",  "2.3.5"
gem "rack",   "1.0.1"

# Additional Gems
gem "sqlite3-ruby"

# Gems specifically for development environment
group :development do
  gem "hirb"
end

# Gems specifically for test environment
group :test do
  gem "rspec"
  gem "rspec-rails"
end