Question regarding post season roster rules

[pogslammer]

If we go with Leake for game 4, adding him to the roster, why does Cueto have to be taken off the roster?
Can it be another player?
Add Leake, keep Cueto on the roster, and just take someone else off. Does anyone know the official rule about this?

[Girevik]

I'm pretty sure it has to be pitcher-for-pitcher in the playoffs. And this is technically a DL, so I don't think you're allowed to switch him out for a healthy player.

Sure, you could fake an injury, but I'd like to think the Reds are above those kind of games.