Read and believe ArmaLube.
It's possible to just hit the main breaker, or to remove the meter (the removed meter is a bit harder to explain to your electricity supplier); but what happens the one time you forget? or when the power comes back and you flick the main breaker before disconnection the genny?
Nope, for a couple hundred bux, do it right.
"Those who have long enjoyed privileges as we enjoy, forget, in time, that men have died to win them."
Franklin D. Roosvelt