github_gem.rb

# lib/github_gem.rb
module Rails
  class Configuration
    def github_gem(name, options = {})
      options[:source] = 'http://gems.github.com'
      options[:lib] = name.sub(/[^-]+-/, '') unless options.has_key?(:lib)
      self.gem(name, options)
    end
  end
end

# Add this line at the top of config/environment.rb:
require File.join(File.dirname(__FILE__), '/../lib/github_gem')