[dcb]

If you are bent on the carb, then you might consider a large flapper valve on the manifold that pops open at high vacuum, and slams shut when you move off idle.

Driveability might take some getting used too, but it should effectively bypass the carb if it is of sufficiently less resistance than the carb throttle plate at idle position.

Heck, a solenoid on a tee fitting on a large manifold port (brake?), hooked up to a microswitch (that also kills the ignition) might be a reasonable carb kill switch setup, allowing you to dfco without sucking so much gas out of the idle circuit. So you hold the switch in and it creates a giant induction leak and kills the ignition. You are usually better off gliding than forced DFCOing thoug.