My friend used a spray collar to train a dog to not bark when he left his apartment. It worked half way through the second cartridge (2 weeks +\-). However, the dog was 25 pounds, and the citronella was pretty strong. I'm not sure how it would work for a really small dog.
You might try youtube, and search teaching your dog to bark. Once they have learned to bark on command it is easier to teach them quiet on command. That way you could let them bark until leashes are on, or after you leave the house, or.... whenever you want. That way they don't have to be "quiet" all the time, but you could at least have a break from the constant sound.
Imagine if you pick up the leashes and have to tell them to bark
We can just see all their faces light up, right? We'll... it is worth a try!