Did you found any solution on adding raleygh scattering effects through p3d as you mentioned by your thread for sweetfx ? It would be great if someone could add this shader as seen om xplane. By the way I already requested this feature on the P3D forum and many users agreed for this :
http://www.prepar3d.com/forum-5/?mingleforumaction=viewtopic&t=6375.3#postid-38172