You would need to use the appropriate 3-way accessory switch; in this case the WS15Z-2, and the WT00Z. The WT00Z does not control a load- it just functions as an accessory.
Please check out the documentation tab to be sure the wiring in your situation will match the manufacturers requirements.
If you have a traditional wiring setup (with traveler), then you might want to check out a Master/Accessory setup
Again, check out the documentation to ensure the appropriate wiring is present. - See more at: http://www.zwaveproducts.com/learn/ask-an-expert/faq/electricity-basics/i-have-an-existing-3-way-switch-and-would-like-to-add-zwave-functionality-to-the-fixture-can-i-use-w?Preview=True#sthash.aQ8ppey9.dpuf