If you mount on a flat surface, perhaps the mirrors could be glued on with epoxy.?.
I wonder if one could use a band saw to cut some dense foam (EPS?) into mounting blocks,
with the precise shapes needed to angle the mirrors?
This is starting to sound like a math job!!
Once a mirror was installed, the whole foam mount could be painted with epoxy. (Like a Surfboard).
If the back of the mirrors and the plywood is primed for the epoxy, then
foam mounting blocks (6"x6") should be pretty solid.. Even with a snow load.
This approach means you won't ever need to make any adjustments..
(You would have to saw the foam in the middle, sand it down and re-glue).
You could do a Fit-Check with light duty spay-on glue.
I assume you are going to come up with a fancy X-Y computer controlled mount??