You could use apps script to add a new recalculation menu item to your sheet's menu and link that item to the function that performs the calculations. That way whenever you want to recalculate you could do it on demand.
For this to work I believe all of the calculation logic would have to exist in the apps script as opposed to using built in sheet functions.
Adding custom menus using apps script.
UPDATE - I kind of missed the point of the original question but I believe my answer still applies. Clearly you don't need a "recalculate" menu item. Instead use the same concept to do the geocoding on demand when the menu option is clicked. You would probably want to add a check to the script on whether or not the column's value was already encoded or not before attempting the conversion.