How would I do this?

I was playing turok last night and I noticed that the T.rex’s neck is a lot thicker and jiggles around more then the one I ported. I tried using a jigglebone but, I read that they won’t work in Gmod. Here is a video of what I am talking about, (http://www.youtube.com/watch?v=fMclCc8_MXo) watch how the neck moves.