gistfile1.txt

Here's what I'm using. Maybe you could adapt it to your case. I have this on a Message model.

def method_missing(method_name, *args, &block)
  if method_name =~ /(.*)_recipients$/
	  self.correspondences.where('recipient_type = ?', $1.to_s.humanize)
	  .collect{ |c| c.recipient }.flatten.uniq
	else
	  super
	end
end