Currently, that can only be done using the Terraform instance type. You can attach option types and provisioning workflows to those to accomplish things like DNS records.
Also, you can achieve this with the service catalog (regardless of the instance/blueprint) as all inputs are manually added to those catalog items, and you would have to attach your own form fields.
I believe that would only cover the option types and not a provisioning workflow. So if all you need is to be able to inject variables at runtime the catalog item method would work.