There are a few good threads on creating seamless textures, however I'm more looking in how I would create seamless edges without really touching too much of the rest of the image.

Let's say I have a map like:

To get it to horizontally and vertically wrap I shouldn't need to touch the middle land mass. However, all the tools I've seen seem to take into account the center far too much.

Things like:
Gimp's seamless filter
Resynthesize filter,
and RR seamless filter

all take into account the middle of an image, making the output a radically different map. instead of just affecting the edge regions.

1. Is there any way to make just the edges seamless?
2. Are there any good links to places where I can learn specifically how to draw seamless map?