just unplug from powerbook
I have the same problem with mine, all you have to do is unplug it from your PowerBook and it will stay powered on but sleep like you want it to, then when you have to use it just plug it back into the back of the PowerBook. I do this all the time since I only use it a couple times a week and also take the PowerBook alot of places so it makes it alot easier. You can even just pull it out of the port just a little bit so that it sleeps since its no longer connected and when needed just push it back in a little and it will wake up and work like a charm. Hope this helps you out.