It is true that most long range bombing sould take the polar route.
In SSS, I'll use another method. I'll use a cylindrical equidistant projection, but with a flatenning because of the isometric view.
However, the map will not go up to the pole, but stop before.
The trick will be that you can go from a square adjacent to a polar cap to any other square adjacent to the same polar cap in 1 turn. And it will be the same for bombers : all the squares near the polar cap are considered adjacents.
It's not perfect, but I think it's a good compromise between reality and playability