Table -component can not do that, but it is a valid feature request (want to write a ticket to dev.itmill.com?).
GridLayout -component supports col and rowspans. Check if it is suitable for your application. If it is not suitable as is, would it be suitable with some CSS tweaking?
That would be a nice feature. Maybe I write a ticket.
I did it with GridLayout and that worked almost as I wanted. I also tried to play around with CSS, but no success. For now, I 'm happy with the GridLayout.