I second the litter in the bathroom idea with this-I'd put a short babygate up to keep the dog out and you can put the food in there, too (just keep it far enough from the litterbox for the cat who won't want to eat something that's too close to their box).
Also, try pine pellet litter... I can't think of any names off hand, but the stuff smells wonderful compared to regular cat litter. When cats pee on it, the pellets dissolve into sawdust. You just scoop the poop and flush it (convenient if it's in the bathroom). The pellets flush just fine. I love this stuff. Seriously. It's pretty cheap, too.