acts_as_class_method.rb

module ActsAsClassMethod

  unless respond_to? :metaclass
    define_method :metaclass do
      class << self; self; end
    end
  end

  def acts_as_class_method(*methods)  
    methods.each do |method|
      metaclass.send :define_method, method do |*params|
        self.new(*params).send(method)
      end
    end
  end

  Object.extend ActsAsClassMethod

end

class Mailer

  acts_as_class_method :send_mail!

  def initialize(params={})
    @from  = params[:from]
    @to    = params[:to]
  end

  def send_mail!
    puts "Sent mail from <#{@from}> to <#{@to}>"
  end

end

Mailer.send_mail! :from => "admin@example.com", :to => "rondy@example.com"

Ruby 1.9 defines "define_singleton_method", so you don't need to use metaclass.

def acts_as_class_method(*methods)  
  methods.each do |method|
    define_singleton_method method do |*params|
      self.new(*params).send(method)
    end
  end
end