usually i either make a bassline i like, loop it for ages in the daw, then tweak lots of filters and fx while it plays. Then bounce it into kontakt, and find the best bits, or in kontakt use velocity-sample start, so that each time you press the key lighter or softer the sample will start somewhere random. Then record a jam session till you find a cool loop. Copy a few channels of it and seperate the bass (so theres a solid sub) maybe send the rest to more fx...play with envelopes on the mids etc tec.
Its sounds like a pain, but can get good unexpected results.