Mike, I think the Wizzy is going to be much louder than the Contra like this. The efficiency of the two speakers is pretty different. Might work for you, might not. But they won't put out the same perceived volumes, and I don't know how you would adjust or blend their relative volumes.
I tried this comparison earlier in the week and posted on it. The Wizzy is much, much louder than the AI cab. I first played them both together and then just the Contra cab alone. It was almost like I couldn't hear it after being hooked up with the Wizzy. If you had the combo, this would certainly be a way to get more volume. If you had the EX cab, I'm not sure it would be worth the effort to use both together.