from what I could tell, there's only one trail leading up toward midnight rock from the top of Castle Rock, and that's the trail I've taken which led me to the ledge. I didn't see another trail, other than the dead-end spur I think I found. Did i miss something obvious?
From Castle Rock I have only seen the one trail which ends right at were you would jump on the left side climbs (North Ramp, Nightingale, etc). But if you go up and around at that gully where that trail ends, you can go up and over Midnight and drop down over by the south ramp. I think most people must just go for Easter Overhang or whatever, so maybe there isn't an obvious trail. Probably just bushwacking, I haven't noticed one at least, but i think I remember walking off that way. I have only been up there a couple times, so there are much more better source for this info that post here...