There is no easy way of achieving this but there are a few options:
1. If the customer zone list does not change often (let's say monthly at most) you can add a sheet to either the Trip History or the Customer Visit report with the complete list and then add a look up that shows TRUE if they are listed among the visited zones and FALSE if not.
2. If they are very much dynamic then:
- Use the SDK, you could use the SDK to build a nice addin that does this comparison in the background and just shows you the zones that were not visited during your chosen time period.
- Keep it simple and run two reports: either a Trip History Report or a Customer Visits report and a Zone Report and then copy the necessary information into one file and do a look up (alternatively you could build a Macro that does this for you).