A few ideas
my first idea is this. atmospheric flight. i know it isn't possible ingame. but there might be a way to simulate it. i think if you where to make a 'system' with solid ground and make 'stations' on the ground which actually look like towns and citys you have a fairly good representation of a planet. then just hijack the docking rings and feed them through to this 'system' make the sky look like an atmosphere and stick the sun a loooong way out and viola! a planet of sorts