Since no one has done this yet, I'd like to offer a few words of caution, based on my own experience. First of all, the nut is a locking nut and will be tight onto the bolt, made even tighter by the heat and corrosion of four years of usage. Secondly, there are several opportunities for making this problem worse: If you try to drive the bolt and nut on thru the hole, you will break away aluminum that is holding the nut in place - which could lead to a crack in the case - not likely, perhaps, but possible. If you are mechanically inclined, then the problem is solvable. If not, or if you have not had experience with removing broken studs or bolts, I recommend you not try to do this yourself. Take it to someone who is experienced: make sure you ask whoever you take it to how much experience they have with such problems. Your local Kawasaki dealer may not have this experience. A good machine shop might be better.
If you are inclined to do it yourself, I see a couple of options:
1. Try either drilling a hole into the end of the broken bolt and twisting it out using a Easy-out tap. This is not likely to work, unless the nut is fairly loosely locked on the bolt.
2. Try Invader's suggestion. I think the problem will be similar to 1, but maybe doing both together would work.
3. Split the nut off the bolt, and then drive the bolt back thru the hole. I like this better but you must be careful cracking the nut. A machine shop would be helpful with this approach.
Anyway, unless experienced here, I recommend finding help.