Nah there's no piggyback port (though I can see why there would have been a need for one) but I think I can manage ok now without a splitter. The main problem I had when I first got the pad was with the position of the ADB port on the AppleDesign keyboard. However with the Apple Keyboard II the ADB ports are right there on the sides. I can use the trackball on the pad in place of the mouse so it's all good.

Still curious to know about the ADB/S-Video compatibility. I read that it depends on grounding, but I don't know how you'd be able to determine this if purchasing one.