You mean when the control doesn’t have the focus?
I had the same issue with mouse wheel, I wanted to send the Wheel delta to the control bellow the mouse, not to the one that had focus. I found this little gem (CaptureMouseWheelWhenUnfocusedBehavior) at stackoverflow.
It traps all app messages and redirect them to some controls you register. With the right modification you can do the same for KeyUP/KeyDown messages.