Putting a "stopper" where you are there in the pic would still allow for other connections to allow air into the engine. You probably wanna get closer to the intake manifold.

While the engine can runaway if you do not install the shutoff correctly, it's not that hard to install...and install it correctly. I think most times when one has run away after a shut off install was simply because careful attention wasn't paid to making sure everything was connected correctly.