Well, I think I originally didn't do this because I based the over-edge scrolling behavior on GIMP, which also doesn't allow this. I looked into overriding the bounds checking, but it was not easily possible because it is buried inside
QAbstractSliderPrivate::scrollByDelta. So I decided to override the wheel event handling entirely, reimplementing part of its logic:
This change still needs to be tested on a system that supports
QWheelEvent::pixelDelta (so with a high-precision mouse, usually). I'll check whether my Mac Mini does, though it has a regular mouse attached to it.