When I'm recording at home on my own, I use a midi keyboard through Sonar to control a bass vst instrument - maybe a midi keyboard is the way to go?

I could just use sonar direct, and click on notes in the timeline with the mouse, but it would be harder work. Do you use a PC? I don't know of an alternative, but then I always use my PC! :D

If you're kinda jamming live, and need something to be a pretend bass player, I don't have an answer....