Add Blank Page

Hi,

my question is following:

i want to add a new page every time a group has odd page number.

This way i can print the report on a printer that has the capability to print on 2 sides.

for example if a group has 3 pages then i want to add a blank page after the last page on the group.

i have tried with new page after after the group footer with the following formula:

if pagenumber mod 2 = 0 then
false
else
true

has anyone an idea???

thanks