Non-database Model for validations

I want to have a model (e.g., a “credit_card” object) that behaves
like an ActiveRecord model in every way EXCEPT saving to the database.

The use case is like this:

  1. User gets a signup screen with a credit card form
  2. User fills out and submits form
  3. Controller receives data and performs validations

4a. Controller presents validation errors to user
4b. Model passes validation, controller uses something like
ActiveMerchant to convey the credit card information to a payment
gateway, but does NOT store the information locally.

In other words, use Rails MVC to control the front end of the use case
(with an emphasis on model validation), while utilizing something like’s services for storing payment information.

Can this be done?

I have not watched them but this site:

has three screen casts about and ActiveMerchant