If you have Victoria or Michael, they have an additional eye part (eyeball I believe) that you normally make transparent to give realistic reflections. If you set its material's transparency slider to zero and apply a spiral texture map, that might give you the effect you're looking for. For the regular poser figures you could arrange a small sphere with your texture over an eye, parent it to the eye, then make the eye invisible. It may even animate with changes in the eye dials, if you position it carefully.