[JLMounce]

I don't know how much actual efficiency you'd be gaining from this configuration. A centrifugal supercharger should also have a boost bypass valve installed that is connected to vacuum. While under low load, the head unit is essentially freewheeling as the bypass valve is open. While in that operational state the parasitic losses of driving the supercharger are negligible.

In a carbureted application, you would then only deal with whatever driveability concerns are inherent with the blow through application.