shared variable. increment it in the group header.
in the 'New Page Before' option, if the shared variable exceeds a value, reset the variable and return true. I would create a section below in the group header so that I could increment the counter in the top section and ensure that the new page is being processed, I have had unpredictable results putting data related formulas in the page header section.
for the new page before formula, something like this should work:
shared numbervar itemCount;
local booleanvar newPage :=false;
if itemCount >2 then (
newPage := true;
itemCount :=0;
);
newPage