Hi,
no, I never got this resolved. I gave up trying to contact Microsoft. Maybe I will make that my mission tomorrow.
According to the document "itsexe" sent, I should be able to get those MAK keys, unless MS are really pushing the KMS model...:
Running Prior Versions or Other Editions
In place of the licensed version, you may run prior versions or lower editions in any of the OSEs of the licensed server. If you have Windows Server 2012 Datacenter edition you will have the right to run the bits of any prior version or lower edition (Datacenter, Enterprise, Standard or Essentials). If you have Windows Server 2012 Standard edition, you will have the right to run the bits of any prior version of Enterprise, Standard or Essentials edition. You should remember that the ability to run previous version or edition bits does not change the licensing or support terms in which you can use the product; the purchased product (Windows Server 2012) rights apply. This means that the license will continue to cover two physical processors and the virtualization rights do not change.