Hi,
If I understood correctly, then you want the group policies (parameters) to be pushed by the AD and not by the concentrator. In that case you need to create the group on the concentrator as 'External'. But in order to use it, you need the IAS service running on the AD server so that the protocol being used is RADIUS. On the AD, there is no option to configure the group policies.
HTH,
Please do rate if it helps.
Regards,
Kamal