Hello,
I don't think, that this is possible as a stored query.
I would be able to provide you with the following solution:
Adding a member count column to the grp object, and display this column in the group list form.
This column would be sortable, that means , when sorting ascending, you would see all groups without members (member count = 0 ) at the top of the list.
A bit tricky, I know, but the only chance I am aware, to find these groups within the Gui.
Using reporting capabilities would be another way to go.
Let me know, if you're interested
Regards
.....Michael