I'm confused by what is difficult. In this case I would make the UX allow the native scroll trigger to operate and then add a zoom trigger. If you make the zoom triggers to be both ctrl+click and two finger pinch then it will work across all devices (ie. mobile/desktop/touchpad/mouse).

I agree that it will be great to be able to target touch pads or mouse/keyboards but I believe it is pretty simple to fix the UX on this app.