Adding #with to ActiveRecord 3.2.13

active_record.rb

# config/initializers/active_record.rb
module ActiveRecordRelationExt
  def self.included(base)
    base.send(:attr_accessor, :with_values)
    base::MULTI_VALUE_METHODS << :with
  end

  def with(*subqueries)
    return self if subqueries.blank?

    relation = clone
    relation.with_values += subqueries.flatten
    relation
  end

  def build_arel
    arel = super
    arel.with(*with_values) unless with_values.empty?
    arel
  end
end
ActiveRecord::Relation.send(:include, ActiveRecordRelationExt)

class ActiveRecord::Base
  class << self
    delegate :with, :to => :scoped
  end
end

that's quite neat, why don't you create the pg-rails gem?