If you're going to add instant espresso, I'd make it up with water, boil it, and leave it covered to cool. (You can speed that a bit with a water bath in the sink, or something.) Then just pour that into your fermenter gently.
As a sanitation rule-of-thumb, once the wort is cool, you want to avoid taking any of it out and then putting it back in the fermenter with the rest of your batch. Too many chances for contamination! The coffee will diffuse on its own given time, and especially if you're racking it any time soon, that's guaranteed to mix it thoroughly.