This isn't politically correct for the animal rights folks but you could put some feeders in there with an auto feeder (set way low). You will likely have a few die and become ammonia themselves. Please don't flame me I know this isn't optimal, its just one way to do it.
There are some devices that can be used to add a few drops of anything on a daily basis, but probably not worth the cost.
There are some devices that can be used to add a few drops of anything on a daily basis, but probably not worth the cost.