you'd want to use corriander seeds. And both would go in at flameout or towards the end of the boil.
I did a few brews at 4 Pines Brewery a while back - we used 150g corriander seeds, 150g orange peel in a 500L wit, and it was barely noticeable... So for a 21l batch... maybe about 10-15gs of each?
Could be wrong though, have never used these things brewing at home