Drop-down filtering of object type metadata

Hi community, 

I am trying to find the best way how to make filter object types drop-downs. In our case, we have an object type representing Countries. We use Country metadata in different document types and we need to apply different filtering in different cases. My approach originally was to use automatic and effective permissions on object types and to apply permissions based certain filters we are getting from our database. So drop-downs of countries were filtered always according to those effective/automatic permissions. This was fine until we get requirement to open countries drop-down for specific document types. 

The trouble is if I remove effective permissions on object type I will satisfy certain document types where I need to provide all countries. Unfortunately other document types where I need to apply our country-level permissions (for certain document types, people should only see subset of countries in document types). I would need somehow to filter countries in other document types based on specific filter. I am wondering how to do this.

Does someone have some ideas about this one? 

Thanks.

Dejan