I think what people do (I'm assuming) is just use whatever the recipe calls for in dry-hopping - only instead of dry hopping in the secondary, they're doing it in the keg. For example, I've got a recipe for a Racer 5 clone that calls for dryhopping it with an ounce each of Columbus, Centennial, and Amarillo for a 10 gallon batch. Next time I brew it, I'm just going to follow what folks have been doing on here. I'm gonna skip that dry hop, but when I put a keg on, I'll put a half ounce of each in a bag in the keg, and start the carbing.
By the time the keg's carbed, the dry hopping should have hit peak happiness!