You can draft a face with reflect lines as neutral lines from which the resulting faces will be generated. You can also trim the material to be created by defining a parting element.
The Draft.x dialog box is displayed and an arrow appears, indicating the default pulling direction.
The option available after the Face(s) to draft box lets you edit the list of the faces to be drafted.
Contextual commands creating the parting elements you need are available from the Parting element box.