it is possible.... you just gotta lock the camera to a unit. it mite lag more on slower pc's...
i cant remember how to do it...
dl a map with it in...
im not sure if the Doom map is protected or not, if it aint take a look at the triggers. I know the instagib maps have a 3rd person view, you could just alter the zoom to make it seem 1st
hope i helped :|....