We could use a camera mounted at the of the case (might need to be very well centered?), to calibrate the galvo the the edges of the build plate. We would then known the offset for the entire border. The inside portions we would still require some calibration for, but perhaps small holes in the build plate would allow a finer calibration to work, but not let too much resin in (we would need to fill the holes or resin would fill it the first print).
We could use a camera mounted at the of the case (might need to be very well centered?), to calibrate the galvo the the edges of the build plate. We would then known the offset for the entire border. The inside portions we would still require some calibration for, but perhaps small holes in the build plate would allow a finer calibration to work, but not let too much resin in (we would need to fill the holes or resin would fill it the first print).