Create an unsuscribe address under an own dedicated IP address

We have licensed a dedicated IP address which is used for sending out mails from Marketo Engage to customers and leads. We would like to create an unsuscribe address under our own dedicated IP address to have just one IP address for different services. To only way to do this is by updating the branding domains which would update the domain for all emails. However, we would like to update just the unsubscribe address which is currently not supported.