Would it conceivable to toggle the option to switch between a map with limits and a circular map? I think it was possible in Civ 4, but I havent played in so long.
I don't know about Civ IV, but Civ II had the option during map generation to switch between a flat map (no wrapping) and a cylindrical (East-West wrapping) map. Whichever you chose was what you'd get for the entire game on that map.
But I think in GC environment getting "fenced" is... a bit artificial. I mean in SoaSE or Endless Space we had "links" between systems. GC3 is somewhat free roaming map, so...
It's not like wrapping the map makes the environment any less artificial. In the case of a North-South or an East-West wrapping, you still have 'fences', in your phrase, on the other sides; in the case where all borders wrap around to the other side the game map essentially becomes the surface of a sphere. Neither of these is particularly more realistic or less artificial than the flat map would be; regardless of its form, the game map is just a representation of a region of special interest, rather than a map of the entire galaxy, or even of a significant region of the galaxy.