I assume someone must have had this request before, but I don't find the option in the code, so before I develop it on my own:
How do I map a category_tree to an object_type ?
As acs_object_types are not objects themself, the obvious way does not work. Two solutions pop into my mind:
a) Make object types acs objects. This has the benefit of solving my problem as well as allowing default permissions on object types (e.g. you can edit all tasks, but not the projects). But I'm sure there are many many reasons against it which I just don't see.
b) Extend category tree map to include an object_type, allow the object_id to be null and change the whole code to take care of that.
c) create a custom "dummy" object for the object type which I use to map against. Then in my code make sure to query against this dummy object instead of the object_type or the package_id