Spots in non-rectangular shapes

GoJS
3

My current node template (simplified) looks like this, where obviously ‘Rectangle’ changes based on the type of node as seen above.

   $(go.Node, 'Auto',
    	$(go.Shape, 'Rectangle'),
    	$(go.Shape, 'Icon1'),
    	$(go.Shape, 'Icon2'),
    	$(go.TextBlock)
    );

I can change the template if necessary. I’m assuming that I want the icon positions to be relative to the node shape, because, in the case of the diamond for example, I want to put the icons in the top and bottom corners of the diamond.

But, as far as I’m seeing, the normal Spot properties are just locations within a rectangular area. I need to place the icons outside of that rectangular area – into the corners of the diamond.