Not the dryest by any means but gets the job done

a_model.rb

class BulkOrder
  
  include ActiveModel::Validations
  include ActiveModel::Conversion
  extend ActiveModel::Naming
    
  attr_accessor :amex, :billing_address, :billing_city, :billing_company,
                :billing_email_address, :billing_fax, :billing_phone,
                :billing_state, :billing_zip, :bulk_order_date, :check,
                :corporate_gifting, :corporate_loyalty_program, :credit_card,
                :customer_number, :discover, :employee_incentives, :gift_card,
                :initial_total, :mc, :non_profit_fundraiser, :overall_total,
                :processing_fee, :quantity, :requested_brands, :shipping_address,
                :shipping_city, :shipping_company, :shipping_fee, :shipping_name,
                :shipping_phone, :shipping_state, :shipping_zip, :subtotal, :unit_cost, :visa
  def initialize (
    amex="", billing_address="", billing_city="", billing_company="", billing_email_address="",
    billing_fax="", billing_phone="", billing_state="", billing_zip="", bulk_order_date="",
    check="", corporate_gifting="", corporate_loyalty_program="", credit_card="", customer_number="",
    discover="", employee_incentives="", gift_card="", initial_total="", mc="", non_profit_fundraiser="",
    overall_total="", processing_fee="", quantity="", requested_brands="", shipping_address="",
    shipping_city="", shipping_company="", shipping_fee="", shipping_name="", shipping_phone="",
    shipping_state="", shipping_zip="", subtotal="", unit_cost="", visa="")
    @amex = amex 
    @billing_address = billing_address
    @billing_city = billing_city
    @billing_company = billing_company
    @billing_email_address = billing_email_address
    @billing_fax = billing_fax
    @billing_phone = billing_phone
    @billing_phone = billing_phone
    @billing_zip = billing_zip
    @bulk_order_date = bulk_order_date
    @check = check
    @corporate_gifting = corporate_gifting
    @corporate_loyalty_program = corporate_loyalty_program
    @credit_card = credit_card
    @customer_number = customer_number
    @discover
    @employee_incentives = discover
    @gift_card = gift_card
    @initial_total = initial_total
    @mc = mc
    @non_profit_fundraiser = non_profit_fundraiser
    @overall_total = overall_total
    @processing_fee = processing_fee
    @quantity = quantity
    @requested_brands = requested_brands
    @shipping_address = shipping_address
    @shipping_city = shipping_city
    @shipping_company = shipping_company
    @shipping_fee = shipping_fee
    @shipping_name = shipping_name
    @shipping_phone = shipping_phone
    @shipping_state = shipping_state
    @shipping_zip = shipping_zip
    @subtotal = subtotal
    @unit_cost = unit_cost
    @visa = visa                 
  end
    
  def persisted?
    false
  end                      
end

Posting on an old gist, but to get rid of all those instance var's try Virtus: https://github.com/solnic/virtus