Footer callbacks and multiple rows

Hi Guys

I started playing with callbacks today, mainly to calculate some column totals on redraw so I've been using the fnFooterCallback function. I have it working great totaling up some columns, but my question is, does the callback support multiple <tr>s in a <tfoot> ? I'd like to have subtotals for each column in one row in the footer and then some group totals in another. Can the callback handle that?

Thanks
Paul