One way to achieve it would be for me to remove the file plugins/system/akgeoip/db/GeoLite2-Country.mmdb and replace it with a link that point to (for example) /var/GeoLite2-Country.mmdb but I would have to do that on each site.
Then I thought, well if the Geolite plugin gets updated, or if someone clicks the "Update the Geolite 2 country database" button, that link might well get replaced or overwritten (or give a permission error to the person pressing the button).
It might be nice for the Geolite2 plugin (and/or Akeeba) to have an option to look at a central database file such as /var/GeoLite2-Country.mmdb so we only need to do one update per month instead of update every site.
Just a thought. :-)
Brian
Brian Craigie Wishaw, North Lanarkshire ML2 0PS