With your experiece and knowledge concerning turbofan and turbojet engines i doubt you would put your hands anywhere near N1 stage unless any source of bleed air was unavailable.
You are right Capt Inop, however on a live aircraft full of passengers the APU will be running and the packs doing all they can to keep them happy.
The luxury of isolating the engines/start valve etc is often not available when slots are at a premium and the station manager is standing behind you impatiently tapping his/her foot.
It is the way of the new world unfortunately.
