If you add a canister with appropriate check valves to prevent losing vacuum back through the pump when off, then your vacuum needs will be served first by the canister, and the pump will run to keep the canister charged, like the air tank on your compressor. The canister will delay the start of the pump a little bit, but will also extend the run time of the pump by the same amount of time once it starts. The only advantage you might gain is one application of the brakes if your canister is charged, and your vacuum pump fails to start, seems to me.