I like this idea. Obviously few theists will be swayed by it, since they will continue to misunderstand what a theory is , and god's existence isn't a theory to them. I guess it's not really a theory to anyone since it isn't fit to be called a theory in the way that evolution is.
My go-to rebuttal when the word theory is used as an argument against evolution is that gravity is also described by physicists as a theory. It's not completely understood, but it's effects are readily visible. The same is true of evolution. I posted something to that effect on here and someone suggested that my point boiled down to "if you don't believe in evolution because it's a theory, you should jump off a cliff."