Google is our friend:
From HomeBrewTalk Forums:
Chocolate Espresso Stout and
Same Recipe More Information; Hoppage: Chinook .5oz@60min, 1oz@20min, Saaz 1oz@5min. He estimated 50 IBU.
Brewery.org:
Espresso Stout; Hoppage: Northern Brewer 7.2% .5oz@60min, .5oz@15min. Estimated IBU: 19.95.
ineedcoffee.com:
Espresso Stout; Hoppage: N.Brewer 1.5oz@60min, 0.5oz@5min, Willamette 0.5oz@5min. Estimated IBU: 45.39.
beeradvocate.com:
Double Chocolate Espresso Stout; Hoppage: N.Brewer 1.5oz@60min, 0.5oz@15min. Estimated IBU: 53.92.
whitelabs.com:
White Labs Espresso Stout; Hoppage: Fuggle 1oz@75min, Centennial 0.4oz@75min. Estimated IBU: 31.53.
So, if your wife does not like hoppy bitterness, my vote would be for the Brewery.org Espresso Stout. That and it looked like a good tasting recipe to me. On the other hand, I have no idea how good its grain bill or anything else looks, you would have to check with others.
Either way, there you go, a lot of recipes to pick and choose from. If you boiled the coffee in the wort (I would consider last 5min, maybe longer), you would definitely get its bitterness. If you put it the secondary, you will get its flavoring (cold brew coffee), but not as much bitterness. Which way to go? Well, if you made a low hopped beer, I would consider putting it in the wort and possibly also in the secondary. If you made a high hopped beer, I would just put it in the secondary as a flavoring.
Again, no idea, I'm making this up as I go here and am just as curious as you about what would work. If I destroy your beer, blame yourself, but let me know if it is good!
On that note. For adding to your current beer? From looking at those recipes, I would go with between 20oz and 32oz brewed espresso or coffee into the secondary. How much depends on just how bitter the beer is already and what other flavors you are trying to overpower. Never hurts to put less in, taste, put more in the next day - as long as you keep things sanitary.
From INeedCoffee, I would trust their advice:
For this recipe, we will brew 16 shots, or 16 oz of espresso. Add this to the wort. I should mention the importance of the brewing of the espresso. I used a Starbucks Barista Home Espresso machine to make espresso. I firmly believe that attempting to use espresso prepared by a steam driven machine will not give you good results. Some recipes for so-called 'espresso' stouts call for adding cracked coffee into the boil, or even into the carboy during fermentation. These beers usually end up having a taste of over-extracted coffee. Brewing espresso properly, however, preserves the integrity of the espresso flavor even after weeks in the bottle.
However, I cannot see why you can't add the shots to the secondary, if you sterilize them (which they should be, it's boiled water).