I doubt the water blown diffuser would work in that set up.
One use which is could be used for is a seal right?
You could use the water to effectively create a wall between the tyre and floor/diffuser area, to reduce the magnitude of the effect of tyre squirt. I doubt it could be used in a way similar to the EBD. This used high velocity flow to extend these vortices if i remember correctly.
(Shelly's theory, image courtesy of DRCorsa in the diffuser profile thread).
I also doubt the 'double diffuser' would be effective at all. The air feeding it is most likely very turbulent and has a lower energy than the air in the main diffuser, unlike in the DDD's of 2009/2010. I also doubt your use of the starter motor hole is legal. Only one hole is allowed, I can see two, a big one (too big for the regulations) at the back of the diffuser, and the intake to this second deck. I'm skeptical on its legality and performance.
Car looks nice though.