you are limited to installing a hitch and using a hitch mount rack or a roof mounted carrier trays. Doesn't the euro Mz5 come with roof rack? If so, you would need cross bars and roof mounted carrier trays. I have both and the hitch system works WAAAAYYYY better. BUT if you already have the roof rack, the cross bar and carrier tray could be the easiest/safest route with minimal cost that you can carry over to other cars. Limitations are that it can be a pain to secure the bikes up top and you need to be mindful of low clearances.
I also have an old tail-gate bike carrier. They work perfectly fine for up to 2 bikes. Used it on my previous sedans and Miata with no problems. But that are not suitable for Mz5 due to the spoiler being in the way.