I know very well that it is possible, but it would be very difficult and would take a while (I'm guessing). Especially if you would have to make the model yourself. I'm not sure how you would get something from the Wii or the Xbox360 or whatever into your computer with the right kind of file to be able to work with it.
Like I said, I don't know the specifics of how you would do it, or if it's possible, but you might have to make a custom model, give it custom animations (not sure if any current animation would work with Nightmare - I don't play SC) texture, colour it, whatever else all the model editors do. But I am sure that Xayo or schlumpf (spelling?) could do it if they wanted to.