Thank you so much!There is another current thread from a member that bought a talking skull from fright props and mounted it on a Costco skeleton. In his post he has a video where he shows how he attached it. Check out that thread. I think he used a threaded rod and zip tied it to the skeleton.
http://www.halloweenforum.com/halloween-props/135241-i-got-new-talking-skull-frightprops.html This is the post. It is near the end of the video.