Cover the planet with your clouds, disable the atmosphere node(the entire node, not just 'render atmosphere' boxes, those checkboxes found in various places would take away the clouds from the render as well.)
Go to the Planet node and un-check 'Render Surface', copy the planet coordinates, with the little box menu selection to their right and paste those coordinates into the camera position. Reset your camera's rotation values to xyz=000 and, if using TG3, do a spherical render. If using TG2, there are various tutorials here about cube rendering for panoramas(I'm sure you'll know but that's just 6 different renders, each facing in different directions, that map seamlessly onto the faces of a cube).