Just a bit sideways from the Q: I would seriously question that approach and rather propose to follow more minimalistic approach giving only grants that are needed. In addition, there is no way to grant certain operations. For example, in order to truncate the table, user must either own this table or have DROP ANY TABLE privilege. Are you ready to grant DROP ANY TABLE? ;-) Of course, there is a workaround to write a PL/SQL procedure.
Something like this GRANT ALL OF a TO b;
-- Best regards, Alex Gorbachev