How to run a Rails application in stone?

I'm not sure that such a thing is very common, but I keep trying to create gems that are just wrappers around the Rails application.

My gem will have a generator to create config.ru, but the Rails application will live inside the gem lib directory. I need to know how to "embed" a Rails application and configure it so that it can run inside the gem.

For instance:

$ mygem new project

mygem created a directory called "project" with the following files:

project/config.ru
project/widgets/
project/foobars/

My gem will also create some directories that need to be added to Rails one way or another so that I can access the code in these directories from a Rails application living inside the Gem.

Any help or advice you can give me will be appreciated.

, Rails Rails. Rails-, , ( rails), , Rails .

: , . gem lib.

$ bundle gem my_gem && cd my_gem/lib
$ rails new my_gem --skip-bundle

:

my_gem/
  my_gem.gemspec
  bin/my_gem
  lib/
    my_gem.rb
    my_gem/
      version.rb # generated by bundler
      # the rails app:
      app/
      config/
      Gemfile
      ...etc

Rails, , Rails Gemfile, gem Gemspec, , assets Gemfile.

# Rails Gemfile
group :assets do
  gem 'sass-rails',   '~> 3.2.3'
  gem 'coffee-rails', '~> 3.2.1'
  gem 'therubyracer', :platforms => :ruby
  gem 'uglifier', '>= 1.0.3'
end

# gemspec
Gem::Specification.new do |gem|
  gem.name          = "my_gem"
  # ...
  gem.add_dependency 'rails', '3.2.8'
  gem.add_dependency 'sqlite3'
  gem.add_dependency 'jquery-rails'
  # how to add the assets group gems?
end