(7.0.2) EWM Filtered List of Categories for Custom Attribute

If I create a new custom attribute for a work item with "Category" type, is there a way, in the UI, that I can filter the categories visible, based on, say, the top level category?
i.e. if the project's categories are:
Cat A
- Cat 1
- Cat 2
Cat B
- Cat X
- Cat Y
If I have a custom attribute of type "Category", is there a way (other than using teams visibility) to filter the list of visible categories to only those under Cat B?
This would be a handy way to have some project-level customisation when using a centrally shared process area.
Thanks