as far as I know fields like formulas or statistic fields are only calculated when they are visible in a layout
Visible in Layout Mode that is,
the new FM13 feature allows to hide an object based on a calculation, so it will still calculate when hidden (otherwise it wouldn't know when to re-appear).
I think you can put it in a popover. Try. I as a SE that question. I dont remeber what they said exactly, but I got the impression the popover would work