No, you can't.
Since the breakdown voltage will never be identical between the two zeners, one diode will always swamp out the other and conduct the most current, until it burns out. Then the other diode will start carrying the load until it burns out, too.
Adding a resistor in series will help distribute the current more evenly. But unfortunately it will also add a linear section to the curve and the reason you're using zeners is specifically because they are NOT linear. You'll be destroying their ability to sharply clamp voltage.
Find a bigger diode.