What about a local newspaper ad, explaining how this beautiful sweet cat needs a loving 'one cat' furever home with a cute picture ?

That way you can reach local people who are not yet cat owners.

Maybe you could put your telephone number on the advert and interview people over the phone and just gives the nice people the shelters address?

Ps.

I am sure he's not depressed because of what you did. It just wasn't a workable situation. This way is the best way for dear Oliver to be spoilt rotten at his new home.