+VE shapes are fine and recommended.
You can copy the Board Outline, for example, with Edit>Z-Copy, set the Options for the Destination Class and Subclass, like ETCH and GND, create a dynamic shape, set the "contract" option to contract the shape by a fixed amout to be inside the shape being copied, then left-click on the boundary of the source shape. A new shape will be created. Right-click>DOne to accept. To assign a net name, use Shape>Select Shape or Void, left-click on the shape just created, go to the Net Name entry in Options and use the "..." button to browse the design nets for a net to assign, OK back through the net selection and right-click>Done to complete the assignment. Repeat for the other shape.