Simply setup your groups as per my previous post, then use the following SQL at the database level to perform the assignment to the user account in SU01.
NOTE: The script will apply each group it finds to the user accounts. If more than one group is assigned to a user, then only one of those groups will be used. The order will depend on the order of records returned in the inline cursor.
set serveroutput on size 1000;
CURSOR c_ug IS SELECT BNAME,USERGROUP,MANDT FROM USGRP_USER;
FOR ug IN c_ug LOOP
UPDATE USR02 SET CLASS=ug.USERGROUP WHERE BNAME=ug.BNAME and MANDT=ug.MANDT;
DBMS_OUTPUT.PUT_LINE ('User: '||ug.BNAME || ' Group: '||ug.USERGROUP);