From what I can see I don't think you can. It seems like G.projector down-samples the map image. I just did a test with the orthographic projection and zoomed in. I had drawn a small but very sharp and readable bit of text. When I brought it into G.projector and zoomed in it was not clear and crisp.
I think others have used G.projector to get the map projection they wanted and then redrew their maps from there.