I don't know why I assumed that a horsehair bow would only work on steel strings. Not true! I just purchased an inexpensive bass bow and found out that the Walkingbass is bowable! I need to get some bass rosin (regular violin rosin works, but bass rosin is softer and stickier and should work much better). I will also need a lot of practice! Bowing is a whole new technique for me, and there appears to be a learning curve. I am also going to make myself a new saddle with the middle string higher than the two outside strings. This will allow me to play all three strings independently of each other.
My wife uses "Jim Bows" on her hammered dulcimer at times. A new technique needs to be learned, but you can sustain notes quite well. The bowing part is a delrin rod that you put rosin on like a violin bow. It has enough curvature that she can bow individual courses of strings.