John,
You're making the twisted leader construction much more complicated than it needs to be. One of the primary benefits of tenkara is that you can keep nearly all the line off the water. If the line is off the water (and there are no guides to foul) there is absolutely no reason why it has to be knotless. Twist three-foot segments and knot them together. Also, that gives you lots of flexibility with respect to line diameters and segment lengths to get a taper - no need to fold it over and twist again. I make horsehair lines that are knotted at rougly two-foot intervals. The knots are not a problem.
Sorry to hear about the rod and the finger. Send the rod to Tenkara USA. I don't think anyone's broken a grip section before, but Daniel might be able to get you a replacement.