I would try to geocode directly in your spreadsheet. I haven't tried
it, but there's this slightly older tip on doing so:
http://apitricks.blogspot.com/2008/10/geocoding-by-google-spreadsheets.html
There isn't a great way to do this in Exhibit as geocoding (converting
addresses, etc., to points on a map) is commonly a paid or limited
service, so it wouldn't be something you should run for every item on
every visit to your exhibit. I can imagine a separate script+page that
reads from your spreadsheet and talks to Google's geocoding service,
spitting back just those records without points for you to plug back
into your spreadsheet.
https://code.google.com/apis/maps/documentation/geocoding/
But try finding ways to geocode in the data before it gets imported to
Exhibit.