Base your report on a query. In the query format the string for the address. Concatonate the address lines into one field, use the IIF function to replace an address line with nothing if it is null (or empty).
You'll need a carriage return to create new lines in the query. Create your own function to replace the CR as queries don't ake this.
It would need something to trigger it, ie in the form, "on activate", command button "onclick", textbox "after update", on enter, on got focus, on mouse down ,etc etc
unfortunately it wouldn’t work in a query