If you dispense with realism, why couldn't you embrace the animal shelter?

Just bite the bullet. Say, "I've grown disenchanted with people, they suck. I'm going to dedicate myself to improve the lives of animals instead, who are mostly blameless victims of humanity, and are much cheaper to make happy than a human".

Utilitarianism doesn't really tell you how many dogs is a human worth, so you well can decide that you value dogs very highly, and that's all that's needed to make donating to an animal shelter very rational.