Hi Jain,
According to your explanation, I think that you need to create one calculation column "FYWEEK" base on "Fiscal_Year_Week_Name" as well,
such as "FY10W03" convert to 1003, then you fetch top 5 from analytic view or calculation view where "FYWEEK" <1003 order by FYWEEK desc.
Regarding as input parameters, you can create static list or base on column to input parameters.
hope this can help you.
Regards,
Jerry