valid_mymodel.rb

module MyModel
  extend ActiveSupport::Concern

  included do
    __send__(:include, ActiveModel::Conversion)
    __send__(:include, ActiveModel::Validations)
    extend ActiveModel::Naming
    extend ActiveModel::Translation
    class << self
      alias_method_chain :i18n_scope, :my_model
    end
  end

  module ClassMethods
    def i18n_scope_with_my_model
      :my_model
    end
  end

  def persisted?
    false
  end
end