I stick it in my porter recipes. I tend to make them dry, lighter bodied and coffee noted (sometimes actually adding coffee). Versus my stouts where I tend to go towards chocolate (sometimes with nibs) and sweeter / heavier. But if you're currently fermenting a dark beer with coffee notes... You might just end up with 2 very similar beers.
Something different than the stout, but still suited for that malt... a light brown ale? You could change the hops and yeast enough vs. the porter where they won't feel like the same beers.