A block of wood won't do any good. That will never seal tight enough, not even right at the turbo. You'd need to attach carpet or rubber or something like that to one side so it can make a complete seal. The cap from a spray can will fit very nicely over the turbo inlet, but that by itself won't seal it all the way either. "Blocking airflow" in theory sounds nice, but might not be that easy when you really need it to stop a run away, especially with the air cleaner and u-tube for the turbo in place.

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"The MB W123 is so bulletproof, you can drive them forever. Which is a good thing as it takes that long to get anywhere."
Betsie: 1984 W123 300D (hobby, 280k miles)
Myrla: 2001 Mazda Protege 2.0 ES 5spd (daily driver, 130k miles)
The Turd: 2007 Toyota Camry (wife's car, 118k miles)