AT THE MOMENT I am using a modified idle speed valve and have drilled out my throttle body to allow high air flow bypass.
Probally needs a bit more air but for my "sound effects" it is fine.

As for a dump valve, yes you CAN have ALS with it.
Once the manifold air pressure rises above about -5 psi (still in vacuum) the dump valve shuts !!!

Would reduce lag even further without the valve but from my past experience I am keeing it on the car