My nan had to be on ahigh fat diet a while ago when she was going through treatment for something, here are some idea we were given:

Avocado, nuts(considering there aren't any allergies for bub or the family), nut spreads, olive oil (sprinkle it on veggies/salads/pasta ect...), coconut milk (add it to smoothies ect), egg yolks (make omlettes ect with extra yolks, cream, cheese and some bacon...a very high fat meal!!), high fat fish (tinned tuna/salmon in olive oil are good, include the oil with it when using it, though be aware of mercury levels), add full fat powdered milk to drinks/smoothies homemade cakes/muffins milkshakes, dried fruits especially bananas

HTH