extracting code to a module, failed

Dear all,

I wrote a piece of code with which I can copy models and their
associated models as new database entries. Now I want to extract this
code so I can easily use it in other projects/models.
What I have:

class Foo < ActiveRecord::Base
  cattr_accessor :non_duplicatable_columns
  self.non_duplicatable_columns = [self.primary_key, 'created_at',
'updated_at','created_on', 'updated_on'] + self.column_names.select {|
column_name| column_name =~ /_id$/}

  def copy
    copy_columns = self.column_names - non_duplicatable_columns
    a = Hash.new
    copy_columns.each {|cc| a[cc] = self.send(cc) }
    clone = self.create(a)
  end
end

Naively I thought I could copy-past this code in a module called
Duplicatable and include that in Foo. This does not work. Ruby tells
me that the file duplicatable.rb should define Duplicatable. Weird but
I figured out that commenting out everything outside the def copy
block makes it work. However now I lost the cattr_accessor and the
initialisation of the non_duplicatable_columns.

I can place these two lines in an def init ... end but that requires
me to do both the include Duplicatable and a call to init. Isn't there
a nicer way of doing it?

With kind regards,
Harm