As of Three.js r69, a updated version of the OculusRiftEffect can be found here
Currently three.js includes a function that renders a Oculus Rift friendly image to the screen. However, the function is made for the first version of the Rift, consequently it will not work with the updated DK2 version.
In order to get it working with the DK2 version, only a few lines of codes needs to be altered.
The updated function may be found here.