product.rb

class Product < ActiveRecord::Base
  attr_accessor :publisher
  
  # ...
  
  before_save { publisher.try(:broadcast, :before_save self) }
end

products_controller.rb

class ProductController < ApplicationController

  # ...

  def create
    product = Product.new(product_params)
    my_publisher = Publisher.new
    my_publisher.on(:before_save, EventListener.new)
    product.publisher = my_publisher
    
    # ...
  end
end