you can try to generate the GUID within the SQL statement, using ORACLE (for example) functions. I guess you will success if the algorithm is not too complex. This way, your insert statement would look like:
Insert into table (c1, c2, ..) values (functions for ID, v2,...)
Although the best practice is to use a trigger before insert which call a database sequence to generate a new guid.
You can also try to make a xslt transformation where you implement the algorithm to generate de guid. You would just have to perform the transformation before calling to dss.
Hope it helps!