On the .67 kernel the exploit used to root the phone got fixed by sony. You have to downgrade the kernel to a previous 4.2-kernel, then you can root and after that flash .67-kernel again.Did you test it? I tryied rooting using previous versions of Flash Tools and none of the methods worked.
But be sure that just kernel is checked in flashtool, otherwise your phone might get wiped.
Xperia ZL, 4.2.2 Stock (.67), rooted