Maya Animation :: Replacing Eyes On Rigged Model?

So I hired a character rigger to rig a model for me, but now I need to update the model. Since it's a more stylized character, I thought that I could get away with a single polysphere for each eye. Now however, I've decided that in order to improve the look of the eyes I'll need to compose it of separate pieces (cornea, iris, pupil).

Here's what I had planned on doing:

1. Change the material attributes on the polysphere to be shiny/more transparent and use it as the cornea

2. Then constrain/parent the iris and pupil to the polyspheres so that they follow properly as the eye moves

I thought that this would be a good way of updating the eye without really messing with the rig, but I haven't been able to get it to work.

My questions are:

1. What's the best way to add the new pieces to the rig so that the eyes continue to function properly and how do I do it?

2. There's another method that I found online for procedurally texturing eyes that works quite well, but it requires the use of nurbsspheres. If I follow this method instead, what's the best way (if different from question #1) to either constrain the nurbsspheres to the polyspheres, or to completely replace them in the rig?

I've sent an e-mail to my rigger requesting these changes, but I was just curious for everybody's input for personal learning purposes.