Chilli, I sympathise.
My father (93) was quite frail when I moved in to look after him over a year ago. I threw out the benecol and olivio and brought in butter and started feeding him whatever he enjoyed and would eat. This included ice cream and chocolate as he'd developed a sweet tooth, but also mashed potatoes and scrambled eggs with cream and butter, cheese sarnies, etc. Now things have changed a bit because I'm looking at the impact of foods on his mental health, e.g. trying to reduce the chocolate volume by using cheese and apple as snacks, and getting rid of wheat. Fortunately he just takes what I give him, so I don't have to worry about if he cares if it's healthy or not, just if he likes/can eat it.
It depends on how food-aware your father is, how much you can 'tweak' standard hospital suggestions without him noticing, but if things get tastier as a result of full fat rather than fat free, most people won't object.