I agree with you that eating high calorie, HEALTHY foods is what should be done to gain weight in CF. An anti-inflammatory diet, rich in foods which support the immune system and provide omega 3 fats is best.
Check out the site I put together (below). I will be adding about 12 recipes from a friend and chef, as well as more of my own, in a few weeks. The recipes are not only healthy but have ingredients which are helpful to digestion, rich in healthy fats, and taste great. I also give some ideas for adding calories only to the CF person as the rest of the family or partners don't need.
I would invest in a good blender and make smoothies to fill in the cracks. We do this for our son and he loves them. I add greens powder, ground flax seeds, egg protein powder and even some MCT oil at times to add calories to his diet. In one smoothie you can get not only the extra calories but immune building nutrients as well.
I also have books listed on the site under resources and links. Basically, I use the same strategy as the Omega 3 Diet book suggests but double certain things for my son (like doubling the oil or mayo just for his portion) or create healthy toppers and sauces for him.
This is a real passion of mine and I hope you can find some great ideas. I enjoy feedback so please let me know what you think.
Warmly,