I'm having the same problem right now, my neighbors have complained to the landlord twice about Jasper's barking. He will pee and poop all over when left alone out of his crate, and frankly I am tired of cleaning the carpet all the time.

I've gotten several good suggestions, but what seems to have helped the most the fastest is working with him on obedience. His confidence is slowly improving, and as his confidence improves, I can leave him for longer amounts of time.

I've been pretending to leave, and standing out side of the door for a short period of time, then coming back in before he starts to bark. I've been able to bring that time up to about ten minutes from about thirty seconds in just a few days.

I've also made a point of ignoring him for parts of the day while I'm home, shutting him in the bedroom while I hang out in the living room, and ignoring him for the ten minutes leading up to me leaving and ten minutes after I get home. The result is that he's not quite so out of control happy about me getting home.

I know you said treats weren't an option, but I thought I'd throw this in there too. I got Jasper an Everlasting Treat Ball, which is a rubber ball which has custom treats that you jam into either end. It takes him about a week to go through one set of treats, and he's a pretty strong chewer.

Since you need a solution NOW, you could talk to your vet about getting him a mild sedative or anti-anxiety medication. These are meant to be temporary measures that you take so the neighbors don't kill your dog while you are working on solving the root of the problem. It sounds like these may be the quickest most effective option while you work on helping him feel more confident while you're not with him. (Star takes one called Clomepramine to help with her panic attacks...she once ate her way through a $2,000 solid oak door during a panic attack!)

I have more thoughts, but for fear of being ripped to shreds for my opinion, I'll PM them to you.