I chew gum for the same reason. If you are worried about the sugar, you can get natural sugarless gum at health food stores. Peelu is the brand I've used before. It's a bit harder to get started, and the flavor doesn't last as long, but it will help with the bad breath.
I'm not sure I agree with the person who posted about awakening the salivary glands will interrupt the process of your body eating off the dead cells.
The thing is, on the Master Cleanse, you are still taking nutrients into your body, through the lemonaid. You are still getting food in, although in a liquid form.
So your body is still taking food in, why would chewing interuppt the fasting process any more than drinking the lemonaid?
Until I find more scientific proof, I would say get some gum for the bad breath.