If you listen to the Wake N' Bake CYBI with Terrapin, I believe he said they add 1lb/barrel of course ground coffee to a fermentor after the beer has finished fermenting and has been allowed a short aging time. They transfer it onto the coffee for 48 hours before moving it off.
They have this dialed in based on their coffee, ground to a certain way, etc. You are probably going to get much more variable results on a homebrew scale--if you do not taste frequently, you can easily overdo it. For this reason, I recommend a cold toddy added to the keg/bottling bucket to taste. About 1/4 lb somewhat coarsely ground in 1 qt of water is about right for 5 gallons--I would make up a little more than that, and definitely add to taste.
When I did a Chocolate Coffee Porter, I did 4 oz of nibs in the primary after fermentation was complete. After 4 days I tasted daily, and when I had the chocolate level where I wanted, I kegged with the coffee as mentioned above. This worked out really well, with the main benefit being you can dial in the chocolate, and the coffee, to exactly the levels you want as opposed to guesswork. The key to these kinds of beers is balance--chocolate from malt, chocolate from nibs, coffee from malt, coffee from coffee all need to be in balance.