It is going to be quite difficult to get a shot where the pupil fills the entire frame on a S35 sensor width-wise, a macro lens will generally go to 1:1 (i.e. life size) or less. 1:1 is only going to give you the eye filling the frame so beyond that you have a few options, including optical enlargement via diopters and doubler and/or shooting on a high density sensor like 6k/8k and cropping in (in which case you can also add a zoom). As a reference point I used a doubler on a 1:1 macro lens to get iris to fill S35 16:9 sensor height-wise.
Don't forget though that a macro lens at 1:1 close focus will have quite a high minimum T-stop (and focal plane will be very very shallow) and addition of diopters and doublers will really bring up the necessary light level. Another consideration is that it is quite difficult to get the eye to be still enough to work at such an extreme magnification (and the camera of course needs to be on rock solid support). The macro lens will shift T-stop as you move out of the close focus range, so you will need to compensate for that.
All in all, I would've thought that the first part from pupil to at least 1:1 would probably be easier to achieve in VFX than optically..
I'd recommend some serious testing before attempting this