There is an easier way. Setup your plane layer as Split/Mixed plane and assign a Net to it. Change to Split/Mixed layer. From RMB (right mouse button) select Board Outline and select it, RMB again and select Create Plane Area and select a net. This will follow your board outline.
You have conflicting priorities there of wanting a cutout in the perimeter shape but pours within the cutout. Without a flood priority on the cutout I believe that is beyond PADS capabilities.
For a quick solution I'd merge the two shapes (inner and outer) into a contiguous polygon with a small gap, and then place a copper shape over the gap. LIke 'C' with a copper shape to close the right side and make it 'O'. This would be easier to understand if I could use an outline font in this response.
I need to create a copper pour border around the perimeter of an oddly shaped PCB.
I've created a DXF that contains two loops (PCB outline and an offset line, the width of the border).
How do I tell PADS to pour copper between these two loops.
If you really want external define of outer and inner edges of this polygon (ie not using PCB outline, and not using pour clearances ) then you can do this by a merge of those 2 polylines into one closed polyline, & copper is filled inside that space.
Of course to make 1 polyline, you need to split/join across the copper area, which makes a 'gap', and you move that 'gap' to touching.
The inner PCB area is now mathematically outside that copper area.
Or, if you are not concerned about outside corner radius, you could create a single copper path around the perimeter. For example, a 2mm wide path 1.5mm inside the border. (extra .5mm space for copper to edge clearance). This is what I do for edge banding for shield via stitching.