Volumetric efficiency is not going to change any differently by restricting intake air than doing the same with the throttle plate. A simpler way to do what you are asking is putting a brick under the accelerator so you cannot push it as far - it would accomplish the same thing.
As far as "leaning out the mixture" goes, remember that the O2 sensor is king of the castle. If for a brief moment you are able to alter AF ratio, the O2 sensor will quickly compensate by adjusting fuel trim. If you are able to significantly alter AF ratio, chances are fuel trim will go all the way to the limit and trigger the check engine light, defaulting to open loop. And open loop is bad.
My suggestion is stick to proven mods. As seen in the link above, restricting the intake probably won't work. WAIs sometimes work, but usually only on MAP sensor engines. t vago used an engine coolant WAI that was pretty interesting:
http://ecomodder.com/forum/showthrea...ant-21863.html