Select Board Outline, Cnrl-C, Cntrl-V and it will be added as 2D-line. Place it on top on Board Outline - RMB - Properties and change to Copper Pour and you can also change Scaling factor if you want to pull it inside from the edge.
I just draw a copper pour rectangle around the board outline. When you pour, it will form the shape inside the outline by the distance defined in your copper rules.
You don't actually need to draw or scale a copy.
On any SM layer, just select the board outline shape (shift click), then RMB, Create Plane Area. It will create the shape offset inside the board by the amount specified in the SM Plane, "Auto separate gap" (set this to the desired value, minus 1/2 the board outline width, a bug causes PADS to use the "edge" of the outline in the calculation).
As stated above, the fill can also be limited to the value set in the design rules for copper-to-board.