you can just toss it (the corriander) in the secondary, just like dry hops, I would think. It all depends on how much aroma you want out of the coriander if you should crush it or not. Are you using fresh orange zest, just out of curiosity? I usually put any spices in the boil, and it tends to extract a bit more flavor and aroma. so you may wan to (like steve said) be a little modest and thenn sample and see if you want to add more.
"Yes, I am a pirate two hundred years too late. The cannons don't thunder there's nothin' to plunder,
I'm an [under] forty victim of fate, Arriving too late, arriving too late."