I'm pretty certain he is needing a LH valve cover bolt, which does screw into the LH camshaft bearing caps.Eagle Mike will sell you replacement bolts, 40mm length with a flat washer works if I remember correctly. I don't think the broken bolt can be stuck in the cam cap.
I recon that he is lucky that he didn't strip the threads from that cap or from more than one hole.
People see that 12mm hex head and just Can Not Resist putting the bean squeeze to them, jeeze.
If Kawasaki had used a 10mm hex head this error would probably be less frequent.
An 8mm hex head would give an even better clue as to the lack of needed torque to seal the rubber gaskets, imo.