I don't know anything about "banking" calories.
I used to subscribe to WW online, but it was too expensive for my budget, too.
I still have the Points+ calculator, and I calculate how many points I've used per day, after I've put them in the SP tracker.
However, I include everything in my calculations, so it's not exactly what WW would call accurate (veggies, fruits, etc., that would normally be zero, are counted in the total cal/fat/pro/fibre calculations).
You COULD calculate each entry, if you wished to do it that way, instead.