FMC displays Magnetic whilst the map displays True wind, so it isn't that hard to move your eyes a few inches to read off the wind from somewhere else.
Would Boeing specify magnetic wind on the FMC for any specific reason? Not much use for plotting on a chart and the variation may well be adrift if the database of variation hasn't been changed (according to our engineering dept). I draw a TRUE wind arrow on the plotting chart at each waypoint since it makes the drift appear more sensible, if you see what I mean.
So, regardless of what is usually done, what is the correct method that should be used?