I have been thinking about this concept quite frequently and come to a solution (may be impractical, but this whole concept is an impractical concept).
1st problem Belt - Change the belt system to a drive system with a clutch, hook this up to an electric servo and wire it into your car, simple.
2nd problem Air going through supercharger while 'switched off' - Instead of bolting carburetor/carburetors on the top of the supercharger hook them up to a two way split system and have butterfly valves control the flow of the air either into the supercharger or a pipe that goes behind the supercharger and into a specialised intake manifold.
Solved.