hmmmm, have you tried maybe applying mineral veil before foundation? Mineral veil is supposed to keep the shiny down (?)
I know what you mean about reapplying without washing your face. That's why I don't use a whole lot in the summertime, I just get to yuky feeling after being out on the boat all day and getting ready for dinner, I just don't want to be bothere with putting a whole lotta stuff on.
But see if putting MV on first might help with keeping the oiliness down. Good luck.