How about the library? You'd have to whisper, or maybe have them read the instructions, but you'd probably have wifi. Maybe even make a couple code changes during downtime.
And I bet there's a decent mall near you with some sort of lounge-type area. I used to manage a retail wireless internet kiosk in a busy mall. We were near the food court, so prime location; we had 1,000 people walking by on any given day. Lots of people plopped down on the couches that were near us; something similar would certainly allow you enough time - they'd often sit there for 20+ minutes.
Could maybe work, but I tried this without much success. The problem with food courts and cafes is that people often come with a friend or coworkers, and came with a specific purpose in mind (getting food, getting a coffee, having a meeting etc.) and so they're much less receptive to user testing in those environments, especially if they have to break off from their group. Also, the presence of any tables immediately makes it possible for people to use their laptops to do their own work. DMV on the other hand offers no escape, and you're stuck there for a long time until they call your number.
Public libraries can work but not as well. Problem is the presence of tables - people come to do work and read and don't want to be disturbed. You also don't get such a steady flow of new people as you do at the DMV. And at a library, if you're talking and disturbing visitors you'll quickly be asked to leave. Believe me, I tried it!