Matrix: 2 Columns In The Row Header

I have the following matrix working:


Measurement M1 Measurement M2 etc....
Unit U1 Unit U2 Unit U1 Unit U2 etc...

Item I1 123 456 120 450
Item I2 111 444 110 440



I'd need to add the manufacturing date of the item to the report. For this I need an extra column next to the row header column (in red) and also a field header (in purple).


Measurement M1 Measurement M2 etc....
Art. Date Unit U1 Unit U2 Unit U1 Unit U2 etc...

Item I1 18Nov2007 123 456 120 450
Item I2 19Nov2007 111 444 110 440


I've tried copying and pasting the first column of the matrix, inserting columns or rows, but I allways end up with an extra grouping level, which I don't want.
The date is the manufacturing date of the item, so it is an attribute of the item, not a separate level of detail.

Anyone knows how to add this extra column to the row header ?

Also, how do I add a column header like "Art." or "Date" in the example above ? I was thinking of placing a text box above the first cell of the matrix, as a kludge.