SAP Web Intelligence -Creating Custom Dimension in SAP Webi Report

Hello ,

I am new in SAP BO,

                         While creating new report,I am using "Week of the year "( which consider days between Sunday to Saturday as one week)  as dimension from the universe in cross tab to split out the data between weeks of the current year .

                    Now i want to define my custom dimension Week of the year which consider starting day of the week  as Monday and End Day of week as Sunday.
                    I created variable as a dimension but its  not working out for me.So it it possible to define custom dimension in sap webi without adding/changing the universe. 

Please assists me !!!