i know what you mean but
i think its a horrible trauma for a cat. think about it, the average cat lives 8-10 years would you want to live 1/20 of your life in prison?
i think the best thing to do is to leave him with a close relative to cry abit... the cat will miss you for a while but if he is in a good place he will soon start a new life
think how hard it would be for a dog, for him its loosing his tribe. still, my parents got a golden retriever that was 6 or something she was very depressed for a month and then adjusted and had a life of comfort (mostly lying somewhere doing nothing eating and sometimes coming to us to be stroked
)