I believe that San Diego/Tijuana and El Paso/Juárez are the 2 busiest border crossings in the Western Hemisphere, so perhaps border patrol and customs employees would frequent the route?
I looked at non-stop flights between Tijuana and Juárez, but it’s only served by Volaris once a day. Either there is not a lot of traffic between the two cities, or maybe there’s an opportunity to pick up traffic from Mexico as well?