I would suggest that your friend simply keeps his database updated using the "Get Recent logs". This way he shouldn't miss any logs, and thus it will limit support questions.
This can be fully automated: set a filter for all relevant caches, and retrieve the last X logs for all those caches.
Next to the above being easier, the alternative you propose, having users send GPX data with caches from geocaching.com in it to your friend could well be considered "sharing geocache data with others", and thus be against the Geocaching.com TOU.
This can be fully automated: set a filter for all relevant caches, and retrieve the last X logs for all those caches.
Next to the above being easier, the alternative you propose, having users send GPX data with caches from geocaching.com in it to your friend could well be considered "sharing geocache data with others", and thus be against the Geocaching.com TOU.