I know there exists such a tool but cannot find it on the web: it's like a screwdriver with a slot in the middle so that you can thread/unthread spokes from the outer rim side rather than with a spoke key.
I have a wheel where the spokes are stuck in the nipples (the hub ends are straight, so the hole spoke/nipple ensemble keeps turning together with a spoke key), if someone has such a tool I'd be glad to borrow it to see if I can get them unstuck (the wheel is buckled). Thanks.