"not a huge amount, just 3-5cm" I hope that's a typo. 3 to 5 cm is 1 to 2 inches! However if you want to move it forword a little, I can't get you carbon, but you can use a Thompson setback seatpost turned around. It will move you forword just enough, not like a Fast-Forword post which just might move you forword 3 to 5.
Want this requirement in carbon? Get a Corima seatpost turned around.