If you are using proper spherical image-maps this shouldn't be a problem.
The simplest solution would be to copy your planets position (the coordinates shown in the planet node, usually, 0, -6.378e+006, 0) to your image map shaders coordinates and make sure you have spherical projection selected.
Alternatively, you could reset your planets position to 0,0,0 and keep the image map shaders coordinates at their default of 0,0,0.
Basically, if the image map coordinates and the planet coordinates match and you have a proper spherical projection image it should work.
That said it is in the nature of geometry that you can't effectively map a plane onto a sphere so there will always be some distortion at the poles. If you can find a polar image map you could cover the poles with a masked plan y projection of just the polar regions.
Finally ... don't sweat what you can't see. Unless you actually need to see a particular region in your shot don't worry if the data is not working there. Just point the camera where the good stuff is and you're good to go.