I had this done recently by a guy in MD who specializes in this sort of thing. Everything he did was to the underside of the seat so the stock shape was retained. He shaved the bottom, customized it a bit to the shape of my ass, and put in some deep pleats at the front which allows it to easily be crushed together which gets my feet much closer to the ground when I'm at a stop. To finish it off he installed a double layer of 5/8" custom formulated gel. He also does full on custom seats in all sorts of crazy materials but I just had the comfort shaping / gel done.
All in all I'm very pleased with the work as my ass doesn't go to sleep anymore and I can much more easily reach the ground at a stop (5'10" and on my 07 ZX6R this was still a problem). Money well spent!
If you're in the DC, MD, PA, N VA area he's a short ride away and you could check out his site at
www.realdealcustoms.com
Not a paid endorser and no kick backs but I do like to plug the stuff that works and rip the shit that don't.