OK went and tried piggybacking, at first just a friction fit test, and yes the difference is great enough to matter
the leds are running at their intended value 15ma, instead of 10, and the entire screen seems more even (not perfect but better) along with the registers sharing current load
worst case and all leds are on at once and stuck, its around 640ma, which is enough to start getting that regulator + heatsink warm with 9v input
so I went back and soldered them, kludge yes, works yes, I know it looks bad on such a thing of beauty ;D and all but ...