If you can read french, this website is dedicated to the ewi and VST's
I made a lot of experiment with Kontakt, and did not get good result. The best expression I got was with the software Wallander instruments. This VST is made for the EWI. Garritan also came out with a bank for the ewi.
Anyways, your best bet is to follow the website's instructions.
He also says that you don't get great results with Kontakt...