I agree, but it is Steve's body (and DNA). We THINK Rolfe put Stephano's "essence" onto a microchip (as he did with Gina) and put that into Steve. So the "real" Stephano is (probably) dead.
If this is true, once Stevano reveals himself to anyone who isn't Kate, Rolfe or "Gina," they just have to knock him out and remove the chip to "kill" Stephano and restore Steve.
The same is true for Gina and Hope.