Question about Parting Lines

Hello guys,i have a simple question :

Is it possible to use a sketch to create a parting line? Because i need to separate a cube into cavity and core but i need a parting line in the center. Problem is,i simple can't find a way to tell the command to create the parting line in the center.

My first thought was to create a plane in the middle and draw a rectangle on it. Then,i would be able to " convert " the sketch into the parting line itself.
I don't quite understand why it doesn't work hehe.

By the way,the cube is just an example.
Oh and guys,if my question isn't very clear,please tell me.

Thanks!

Message was edited by: Laurence Possebon

SolidworksParts And Features