Some setback posts have enough adjustability in the clamp to be possible to run in reverse.


But if you're looking to add 1-2" to an already forward post it seems like you're pushing the adaptability envelope more than actually possible and/or sensible.
If you need such an extreme tweak of saddle position, I'd be surprised if the rest of the bike will let you reach your goal.


Or look if you can buy a seat post intended either for fit bikes or for spin bikes, which tend to have huge adjustability. They'll be a lot heavier though.