Filtering the Selection of User Groups

We're trying to create a new security model based on $USERGROUPS. Under the usergroup node we have created several subclasses, such as departments (to identify users belonging to functional departments), routing groups (which are prededefined approvers and observers list) and design teams (to denote the design team who owns and manages the part; new security model). We've assigned the user group list to a part attribute used to identify the owning design team. However, when attempting to select/assign the design team, the entire user group including all other subclasses appear for selection. 

 

Is there a way to filter the list selection, so user will only see the user group subclass "design teams" and not the other user group subclasses?