Managing membership of local group - Domain Local groups not permitted?

Hi all

I would like to populate the membership of the local Administrators group on certain member servers using the "Local users and groups" feature of GPP.  The object picker does not let me choose groups with Domain Local scope. 

Does anyone know the reason for this?  Is there any workaround?

I can add domain local groups to the membership of the Adminstrators group manually, so it seems strange I can't do it via GPO.

Alexei