Hmm, I give up, what is the trick for eyes?  I can see a way if you add an intermediate bone or if you turn off bending for the head, but these aren't the way figures are commonly rigged.

The "official way" (although I don't see any figures that are rigged this way) is with an intermediate bone:
http://poser.smithmicro.com/tutorials/Characters_rigging.html

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