You might be able to do something with the Group Footer band's Run Expression On Exit. Double-click the Group Footer to see what I'm talking about.
I think you have to call a program from here, but don't quote me. I couldn't get just a command to work.
e.g.,
On Exit runs PrintPageNo()
Activate Screen
? _PageNo
This gives the _pageno as it's leaving the group.
You'll still have to run the report once to calculate it.
Insanity: Doing the same thing over and over and expecting different results.