I don’t think it is what you want anyway. It provides board area free of copper and solder mask (which isn’t what you need!) I think your current path is the only one that is likely to be successful, gerber processing appears to fill in the entire inside of the shape ignoring stroke-width. I was intending on using a pad (made of a circle with a stroke width set) which works in Fritzing pcb view but doesn’t in gerber output (as noted the stroke is ignored and the entire circle is filled in. This works for the usual pad because the drill file causes a hole to be drilled in the pad (the gerber copper layer has a completely filled in interior even though the typical pad has a stroke-width and an empty center), in this case we don’t want a hole in the pad just separation between the two pads and it looks like ground fill is the only way to get that. You may have to live with a not completely circular shape unless someone that know more about ground fill than I do has some ideas.
I think the output is from a ground fill of a circular pcb, and thus I don’t think he has much control of the shapes (although I know almost nothing about ground fill as well 
) It may be that a code change will be necessary to get better results, but I agree the next step should be to upload the .fzz sketch file (upload is the 7th icon from the left in the reply menu and will accept the .fzz file of your sketch) so someone familiar with ground fill (not me ) can have a look at it.
Peter