You should be fine just connecting the motors in serial or parallel in the same way that the z motors are wired. If one motor goes the wrong way, just switch two of the leads to it. I'm curious as to why you're doing this though? Btw, I'd love someone to correct me, but I think these are the pros/cons of serial/parallel:
series pros: lets the max current of the driver flow through both, so you might get more torque for equivalent heating of the driver at lowish speeds. cons: the drivers are chopper drivers, that rely on a higher driving voltage than the voltage you want across the motor, to reduce the effects of inductance at high speeds and push the max current quickly
parallel is just the opposite
