my last idea
i found this fine to help sometimes
i use AF-ON to focus only, and AE-L for exposure...here nothing new!
if you use function Button with "spot", it helps when spot exposure gives better results in shadows.
Sometimes when i'm in manuel mode and with contrasted areas, i have to evaluate speed, focal, iso for correct and general expo.
but if you want to push a little expo quickly, to give more details and light
you can push function (to activate quick spot expo) and push AE-L to get expo on this specific shadow area you want (better medium shadow, this selection will set the level of correction ),
then use AF-ON to focus other area if wanted, and then use shoot button .
this is quite rapid.
in manual mode you can't see valor change in viewfinder (speed, focal), but shoot will be corrected on initial exposure indeed.
if you're in A mode, then you'll see speed change in the viewfinder, this can help to choose a little correction only of exposure.
this is just to test but, i think this can be useful
take a look if you can and tell us your conclusion
i tried to be clear but not so easy to me...sorry for that, not easy to explain, but simple to use
so we can get Spot mesure during the shoot, only by holding function button and AE-L
Best regards Eric