I would go with having him neutered, and see if the problem persists. If it does(which it shouldn't, as a male cat normally loses his desire to spray at the same time he loses his balls, but you never know), see if a kitty-friendly friend is interested in taking him off your hands, and if not, let the Humane Society adopt him.
Just as an aside, there are 4 cats in my house, 2 of whom are neutered males, so I can sympathize with your position, CK.