Do you have a YEAR formula / parameter / select expert?
If so, and you are filtering 1 year only (ie; 2012) I would have GROUP1 as YEAR, and GROUP2 as MONTH.
then write individual formulas along the lines of:
@JANUARYSALES
IF
{@month} = "JANUARY" THEN {TABLE.QTY}
@FEBRUARYSALES
IF
{@month} = "February" THEN {TABLE.QTY}
etc
and summarized these formulas by the YEAR group.
Then simply place these summarys in the GROUP1 header, and stretch the section so it covers 1 page only.
it would then hopefully give you like;
page 1
GH1 - YEAR 2012
January = 1234
February = 234
March = 54232
etc..
page 2
GH2 - January 1234
customer
customer
customer
etc
Of course, this is only how I would do it. There is more than likely simpler solutions than people may be able to provide, ie; shared variables etc....
hope this helps.