you can do option 2 with a foam sheet from a Race Supply place - Dennis Trollope or maybe Demon Tweeks etc.... but these are really not comfortable.
As your seat is thin f/g, I'd go for option 1 and cut a hole in it, this is a better option IMO as the seat pad sits on top of the subframe and there is no stress on the thin f/g seat unit. With the foam pad, you're putting a lot of weight on the seat unit and it may split.
Tim
