MarketPress reporting by category

Hi Folks

Not sure if anyone has requested this yet, but I can't imagine I'm the only user who would need it:

Is it possible to report on MarketPress sales by category in the plugin? Essentially, we have a range of product types which all need to be accounted for separately for tax purposes.

I know the current reporting allows you to export a report to CSV by month. How difficult would it be to allow reporting by month and by category of product (i.e. "show me the value of 'books' I sold in April 2012")?

Thanks
Marcus