If working with the FeaturesCollection component is just not happening, you could always workaround this by parsing the geojson file and generating runtime polygons, with all your properties, using blocks:
Here is an example - with a couple of random polygons added.
geojson.aia (6.8 KB)
(I included a hexToColour procedure which you will need if setting the FIllColor,StrokeColour etc.)
