As Carl noted above, if you're dropping one end just do the other the same amount to keep the rake/trail from being affected. Not sure about the S, but you can't do much more than about 5-6mm more at the front on a base without the fender hitting the fairing. Mine's at -5mm front and -4mm rear at the moment, not for getting feet down which was no issue to begin with, but for overall handling (CoG) purposes. Still testing and tweaking, so it will move around some more (probably back up a smidge at the rear first), but you can drop 5-6mm at both ends with no issues; it's free and it's easy.
If you're really wanting to go lower for feet-down purposes, I'd say abandon the comfort seat idea straight away and look at reshaping/recovering the stock seat so that it would be lower. That and a small ride height drop would give far better overall results than ruining the handling with a big drop at the rear. Again, you don't have much to work with at the front.