Unless something has changed recently since I researched several years ago WOW did not have support for VOD using any third party device. VOD requires two way communication and the Cable Card when used in a TiVo is only one way.
I believe you can call WOW and purchase a VOD movie. They will have to push it to your cable card to allow viewing. PITA IAC.
VicW, Ex-Comcast customer ... And loving it!.