The easy way to add fats is to put olive oil on everything you consume. I purchase rather expensive olive oil ($30-$35 U.S. a bottle...be sure it is date stamped and in a dark bottle). I have developed a real taste for good olive oil, much like one would for wines. I eat sardines and tuna canned in olive oil. I also snack on macadamia nut butter, almond nut butter, and English walnut butter, all with celery. Leftovers are my main stay for lunches with, you guessed it, drenched in olive oil. I supplement every morning with Carlson's cod liver oil.
It really doesn't take a lot of fats to get your calories up there, but they will start making a difference in your appetite.

Take Care