Crosstab - column subreports

Hello,

I'm searching for same advice, hint ... I need to make column subtotals in crosstab

I have crostab like this

                    january 2011      February 2011    March 2013     December 2014     TOTAL

product1               5                         6                    7                         8                    26

product2               1                         2                    3                         4                    10       

Product can be more, and usualy I have data from every month this abowe is only example, also time interval is set by user (report parameters)

everything works OK but now I need to make a subtotal after every year :

                    january 2011      February 2011       subtotal             March 2013     subtotal       December 2014          subtotal         TOTAL

product1               5                         6                      11                       7                   7                       8                              8                26

product2               1                         2                      3                       3                    3                       4                              4               10      

I thing it must be done by adding calculate member, but I can't reach data from dataset since I have crostab in header.

Could someone explain me how to do this ?

Thanks for any help