Filtering 13 months of data by top 5 for current month

Hello,

I am wanting to create a table/chart to display the last 13 months worth of data filtered by the top 5 product categories for the current month.

I have to be able to have this dynamically gerenate, as I am unable to modify the filters each time the report is run.

I was doing this by having a little table to display the top 5 for the current month, and then filtering the 13 months of data based on that table, but this isn't working when I am unable to modify the report.

Is there any sort of formula that I can use to achieve this?

Thanks!

Stephanie