FSG - Colum Set Account Type Question

How do I create a column set where the amount = prior year YTD through a specific period, but not a fixed period. 

Example - Report Ran for Nov-2009

Column Name = Prior Year To Date - needs to show last year's YTD through Nov 2008.  When we have the offset of -12, it did not give us any valid data. 

We need this data to compare to current year to date for the same period. 

Any ideas????

Thanks,

Jean Ann