Have you tried an EBow? I just was given one, and while I can't make any usable sounds with it, I understand there are those who can. It's not really designed to use with a bass, but somebody needs to inform Michael Manring of that fact.
I have one, and have taken a few tries with it. at this point the sounds I am getting are very cool, but very unpredictable. This seems like something that will take a while to get a good feel for. But very fun to play with!!