That thing being a tube is not mentined on the movies. Even if documentaries state that it was a tube, movie goers assumed it was an elephantine trunk attached to its chest. So I think it would not be wrong to make the jockey have a trunk. It fits Giger's disturbing imagery. I would love to see the Alien that came out of the jockey. I saw a "Jockey Alien" in a videogame vid in you tube.
You can see it at 1:21 and beyond for a few seconds (By the way, weird song).