Reform gem: use one model for multiple forms

I am using Reform gem to make a form object for checkout in my web store. I have the Checkout form which contains properties for Order model, which has associations with Address model.

Problem is the Order model has two association with the same Address model:

class Order < ActiveRecord::Base
  #...
  belongs_to :billing_address, :class_name => 'Address'
  belongs_to :shipping_address, :class_name => 'Address'
  #...
end

So I need to set up my Checkout form to use Address model twice. The temporary approach I used to apply was trivial. However it was working fine:

class Checkout < Reform::Form
  extend ::ActiveModel::Callbacks
  #...
  property :billing_address, populate_if_empty: Address do
    property :firstname
    property :lastname
    property :address1
    property :address2
    property :phone
    property :city
    property :zipcode
    property :country_id
    property :billing_address_for_id
    property :shipping_address_for_id

    validates :firstname,
              :lastname,
              :address1,
              :phone,
              :city,
              :zipcode,
              :country_id,
              presence: true

    # provided by phony_rails gem
    # validates phone number to be correct and plausible 
    # without country accordance
    validates :phone, phony_plausible: { ignore_record_country_code: true }

    # provided by validates_zipcode gem
    # validates zipcode to be correct due to country alpha2 code
    validates :zipcode, zipcode: { country_code: :country_code }
  end

  property :shipping_address, populate_if_empty: Address do
    property :firstname
    property :lastname
    property :address1
    property :address2
    property :phone
    property :city
    property :zipcode
    property :country_id
    property :billing_address_for_id
    property :shipping_address_for_id

    validates :firstname,
              :lastname,
              :address1,
              :phone,
              :city,
              :zipcode,
              :country_id,
              presence: true

    # provided by phony_rails gem
    # validates phone number to be correct and plausible 
    # without country accordance
    validates :phone, phony_plausible: { ignore_record_country_code: true }

    # provided by validates_zipcode gem
    # validates zipcode to be correct due to country alpha2 code
    validates :zipcode, zipcode: { country_code: :country_code }
  #...
  end

But it's obvious that duplicated code must be refactored. And there I found that I can't come up with any working solution. My last attempt was like following:

class Checkout < Reform::Form
  extend ::ActiveModel::Callbacks
  #...
  property :billing_address, populate_if_empty: Address, form: BillingAddress 
  property :shipping_address, populate_if_empty: Address, form: ShippingAddress 
  #...
end

class BillingAddress < Reform::Form
  extend ::ActiveModel::Callbacks
  include Address
end

class ShippingAddress < Reform::Form
  extend ::ActiveModel::Callbacks
  include Address
end

module Address
  include Reform::Form::Module

  property :firstname
  property :lastname
  property :address1
  property :address2
  property :phone
  property :city
  property :zipcode
  property :country_id
  property :billing_address_for_id
  property :shipping_address_for_id

  validates :firstname,
            :lastname,
            :address1,
            :phone,
            :city,
            :zipcode,
            :country_id,
            presence: true

  # provided by phony_rails gem
  # validates phone number to be correct and plausible 
  # without country accordance
  validates :phone, phony_plausible: { ignore_record_country_code: true }

  # provided by validates_zipcode gem
  # validates zipcode to be correct due to country alpha2 code
  validates :zipcode, zipcode: { country_code: :country_code }
end

And with that setup

@checkout = Checkout.new(@order)

was giving me the error

undefined method `active_record' for #Declarative::Heritage:0x007ff6ea6fb038

So is there any standard approach in Reform to make things above work? Or can anybody tell what I do wrong? Thanks!