First, you aren't duplicating a layout. You are duplicating a group of records. Your are duplicating a parent record--the layout's current record and easily done with the duplicate record command, but then you want to also duplicate the related records shown in the portal. This requires a scrpt.
The script at the end of this thread is an example of such a script: Duplicating Bill Of Materials (duplicating portal line items)
Ok thanks, Ill modify the scrip to fit my situation.