Bone that faces player?

I’m curious if its possible to make a bone always face the player or at the least, give it a free rotating physics based pivot? I’m trying to re-create the effect from Left 4 Dead’s Puke jar:

82149-puke02.gif

One way to do this (i guess there are several ways), is to use a skeletal mesh with weight paints on the top of the fluid and then use a angular spring/motors to make it swing back.

Thanks for the suggestion aloneball. I’ll look into this as I’ve never heard of an angular spring/motor before.