Unfortunately, the ZD wasn't designed with that use-case in mind. Our SmartCell Gateway products were however (you can think of it as having multiple virtual ZD's each with their own country-code) and should work. You'll want to speak with your SE about suitability with regard to other features you may need.
I've got exactly the same scenario as the original poster. This seems an extraordinary situation where the individual APs - in our case R300s - support the technology but the ZD3000 doesn't allow this flexibility. It seems logical that this setting should be in the Access Point Groups not the System settings. Is there any plan to add this feature in later releases? We are build 9.12.00 build 336.
I would firstly look at what countries your AP's are deployed in and check the regulatory requirements for each country and determine simalrities and deltas between them all (as you are from the Netherlands then there may be a possibilty that they are all governed by ETSI so it may be very easy)
Note: The are only a number components that you have to really think about and here are a few:
EIRP Channel Occupation DFS
Based on the requirements you would have to choose the domain that has all the relevant regulatory requirements.
I would then create a table based on all the requirements for each regulatory domain and create an AP group for each country (changing power values and channel occupation etc. for each group)