If I want to really put weight on a fert I grind up chicken, rabbit, eggyolk until it is a paste, then add a bit of heavy cream [not the pre-whipped stuff] and water it down a bit until it is easy for the stinker to eat. I've brought a few ferts back from the brink of death when they would eat nowt else but that.
If it is in really rough shape, then keep on as you have been doing and wake it up for a feed every so often.
Cat food...personally I think you would be better off with the meats and fats they would normally get, but if you really wanted you could get a good quality cat biscuit w