You could skip the Secret Origins if you like, it's also in trade now so you could just grab that, it retells Jordan's origin with some updates to it and insterts some of the mythos of what's going on currently, but Johns has been building up to this since Rebirth, there's subtle hints and not so subtle hints as to what's going to occur.
If you've read the Sinestro Corps War, there's a couple of issues right after GL 25 that deal with the Alpha Lanterns that are worth picking up, then it goes into Secret Origins, which I explained a moment ago, after that you get into the Rage of the Red Lanterns stuff which is great from start to finish and then Agent Orange which has me drooling.
Over in GLC, there's very few you can skip as far as build up goes after the Sinestro Corps War, and I've been loving the Emerald Eclipse stuff with Mongul running around fairly unchecked.
No matter what, both series are among the best going right now, but if you wanted to skip it all it looks like the Free Comic Book Day Prelude to Blackest Night will answer most of the questions you'd have leading into the big event.