Well, culling the planet into pieces would be one part of it. What I mean is using algorithms to produce heightmaps, then producing terrains from those heightmaps, then deforming those meshes to sphere segments. What you'd need to be able to do is to produce terrains with the same features but with detail that varies with distance from the camera (ie, producing a new heightmap using a segment of an old one).
I can't tell you how exactly to do it, I'm not that good of a programmer. It has been done (
http://fl-tw.com/Infinity/), but the procedural techniques are probably out of DB's league.