You're probably also incurring a lot of liability just by contracting the individual shipper to take an action on your behalf. Say your person is dropping a package that's just off their route to wherever they're going. They pull off the freeway, and BAM get hit by a semi. Congratulations, you're going to be the recipient of a huge lawsuit.
Easy to dismiss that as, "Well how often does that happen?" Accidents happen, on average, one per every thousand driven hours. So if you've got a thousand en route today that are taking more than an hour, you get to have this problem once a day, on average (v weak extrapolation, I know).
Some things can't be done as a lean startup. Some things cost major money before their first day (e.g. airlines, long-haul data services, auto manufacturing). You managed to pick a non-lean industry.