I just had an idea, which I naturally believe to be so brilliant that I have to bring it up:
You said you have to reload the game after generating a new map because that's the only way Civ5 would update it. But Civ5 updating it is not the only way to let the player see it, is it? Reseed could generate it's own preview of the starting area, which isn't very big. I recommend a strategic view in the second-furthest zoom scale, with resources and yield marked.
So what I'm suggesting is that Reseed regenerates the map, create it's own preview of the new map's starting area, shows it to the player, and ask him if he wants to proceed with this map. If yes, reload the game as you do now; if no, generate another map and start over. This would cut down the huge amount of time wasted on reloading games whose map would turn out to be unwanted. And for people who choose to use Reseed, it's safe to bet that the percentage of maps the player would reject right away is very high.
Now, I have no idea if Civ5's graphic engine itself could be used to generate the preview. Off my head, I consider it to be unlikely. But since all the graphic elements are very much accessible to mods, it should not be feasible to construct the preview yourself.