Endnote X6: Smart group and smart sub-group is it possible?

I have a database of 900+ records and have created a smart group of records based on content in a custom field.  I want to create 2 smart sub-groups from this main smart group as follows:

Sub-group 1. Records that have files attached

Sub-group 2. Records that don’t have files attached.

Then when I attach files to records in sub-group 2 they are moved to sub-group 1 and removed from sub-group 2.

Any ideas as to how I might get this to work?