When neither was an option for me, I used to crank the ISO on the meter dial (on the right side of the body when viewed from the front) all the way down to the lowest ISO (50? I don't recall). This would close a four-bladed iris over most of the meter window, reducing the intensity of the light falling on the meter.
Not sure, in retrospect, how much battery life this saved me.
Cheers,
--joe.