Well, another idea
Data Pumn has PL/SQL Interface (see dbms_datapump). so u can wrire a stored procedure, which does the export and is owned by the schema object owner, but grant execute on this procedure to the developers.
If u want to have an idea how such procedure will look like, just make an expdp using the database control and at the last step click "Show script" or whatever it's called button

Good Luck
Boris