I think I suggested something like this elsewhere recently.
I'd use a counter to determine which detail line I was on , and then
a variable to store the value I wanted to move down. (ie Product 1 or 3)
Which I could then display on a line somewhere below.
This is easy when you can put your details in a group and move all the values to the group footer, but may need a bit of manipulation to get the pattern you want.
And you have to be careful about resetting variables back to '' in the right place.