I brewed up a batch of Tuck's "Chocolate Espresso Stout" a couple of months ago, and kegged it a month ago. This stuff is over the top! It's like a chocolate milkshake in a glass.
I took a "handful" of sumatra espresso beans, and dumped them into the secondary carboy. Just dropped them in whole. They sank over a few days, and the coffee flavor is spot on.
This stout is getting better as it ages, the chocolate bitter taste is melding into a smoother espresso mouth feel.
The only problem is that too many people know that this in now on tap, and it's a very special stout that needs to be savored and appreciated.
Sorry for the ramble... just dump them into the secondary... Good luck.