Maybe you could reach in with forceps and pinch off the line from the "T" to the venturi? I thought about putting in a check valve, but then it wouldn't suck oil presidue out of the case breather. Still, I don't see anything wrong with letting some of the after-run oil into the venturi...hit the spinner with the starter and your Saito is winterized...
Steve
Edit: You could also arrange a 'shutoff' type gizmo to shut off the line to the venturi only when you want to. But I still think you'd do fine to flip the model upside down, squirt some oil into the T-fitting access hose, and hit the spinner with the starter. Whether the oil goes into the venturi or into the case, it will go into the engine, which is the objective.