Similar to the Jack In The Box and the Push Puppet aios, this would have a vibrator in it that would pulse (poss. in some pattern), causing the head to waggle. Periodically? Until reset? I have a nice JP Patches bobble head just waiting for some bigger role in life.  I think this would be a very fun project, and very easy if one had easy access to a pager motor (stick it in the head and run wires down the neck).