How to change BEx variable 0FYTCFP

Hi,

I am doing HR report to calculate payroll using user-entry variable to decide which month should be reported. Also I need to show the cumulation result from beginning of fiscal year to the month that user enters, which is a proble for me. BW provides variable 0FYTCFP (Cumulated up to Current Fiscal Year/Period) using SAP Exit, but it is only for current period. Does anyone know what I can do to fulfill this requirement?