Does anyone know if there is a way to add "OK_UNASSIGNED_SHAPE" using skill?

I'm using SKILL to generate some shapes using axlDBCreateRectangle(), converting it to dynamic using axlShapeChangeDynamicType(). I then want to add the "OK_UNASSIGNED_SHAPE" property to the shape. Does anyone know if there is a way to do this?

An example of the code:

shape = list(-1000.0:-1000.0 1000.0:1000.0)

sh1 = axlDBCreatRectangle(shape t "CONDUCTOR/TOP")

sh1 = axlShapeChangeDynamicType(car(sh1) t t)

when I look at properties now for using sh1->?? i can see there is a prop parameter but I'm not able to change it at all. It always reports nil. When I try to read the property of an existing shape that I know has the "OK_UNASSIGNED_SHAPE" property already defined on it I also only see nil for this property. 

I understand there may be a way using axlDBAddProp() function but this doesn't seem to do anything either. I'm at a loss.

Any help is appreciated.