zenith,
Are you trying to accomplish this in ReportStudio? Is there some logic to the sort sequence in the table? In other words will the rows always be returned in the same order.
It seems that you should be able to add a column to the table, "rownum". Then, in you report create a case statement for user_id and filter the data based on user.
Sorry to be so vague. We need more information about your requirements.