No there currently is no way to constrain a enumeration. What you could do is create an object that has the enumeration value and constraint that object based on some Business rules.
Because you are able to constrain objects the dropdown will be kind of dynamic. However this is not less work then the alternative you already provided.
When I started working in Mendix I tended to put everything and its mother in Enums when and where possible.
After delivering 3 application for production I now find that I use Enums strictly for those selection-sets that are pretty much no-brainers, but that for anything slightly more complicated then "gender", I prefer to create a module with "basic" tables and use those to provide the content of a dropdown.
The pro´s for this approach
The cons
As a work-around, the Slider widget on the App Store can ignore selected enumeration values. Do note that this is not dynamic and only client-side though.