Hi Hoang-Phong,
The EyeX tracker distinguishes between eyes in a face and eye-like features. If you put the artificial eyes on an image of a face close to real size, then the eye-tracker will track the artificial eyes. The image does not have to be in color, a black and white image will do. You can use double sided sticky tape or glue to fixate the artificial eyes on the face image. Put the image on a piece of cardboard to make it sturdy.
Hope this helps,
Peter