You can try that, but I don’t think it will work. DH will still note that the domain had been previously hosted at DreamHost, which makes it unable to be used with a new promo code.
The promo codes are designed to be a “one-time-only” and “for new customers only” benefit.
You should write support and explain your situation. They may, or may not, be able/willing to help you. We are just repeating here what we have been told …