I've finally found a solution I'm happy with:
https://www.amazon.com/gp/product/B01H38IIY6/
A plug-in for the OBD-II outlet (power only) to a micro-USB connector, with enough cord to wind through into the center console. $10 bucks. There's a slightly more expensive model with a switch on it--I didn't want that one, assuming the switch would be a likely target for my feet to kick off inadvertently, and that the red switch would be very visible. I haven't tested either of those assumptions, since I only ordered the one--and, if I ever need to "turn it off," I'll simply unplug it. The cord exits the head of the plug at a 90° angle just about exactly where the plastic foot shield on the under-dash is, with enough wiggle room that it could run outside or inside the shield.
Of course, I wanted it inside & hidden. I had to remove a single screw (Torx head) at the rear/left of the shield in order to get the plug in the socket and maneuver my hands to run the wire inside (or you can plug it in directly without removing the screw, if you're happy with the wire exposed). From there, it was simple to route it behind the shield, over to the corner above the accelerator pedal & into the center console. I could've used an extra wrist & eyeballs on my fingertips
for this next part: the hardest part of the whole job was getting it through the holes inside at the front of the center console so it would be inside the storage compartment without interfering with the sliding cover. I used a couple of zip-ties inside the compartment to make sure it stays put (and doesn't get caught up in the mechanism of the sliding door), and reinstalling the single Torx screw was as simple as taking it out had been.
Voila, I now have constant +5V power in my center console, without drilling or cutting. I may yet go that route--or, more likely, hire a professional car audio guy--an install actual USB power outlets... but, for now, I'm in business. The top 1/2" or so of the plug (upside down to fit in the socket) sticks out below the shield--but, it's basically invisible, since it's the same black color as the shield itself. Even if you were to go looking for it, all you'd see is a small "bump" in the shield where there used to be a hole. The entire wire is hidden, unless I go digging for the Pi in the center console.
The power plug is directly in the Pi's power-only USB; and I did the electrical-tape trick to make a data-only cable to plug the Pi's data port into the car. It's been up & running for two weeks now. During that time, I've done multiple local drives, a ~1,500-ish mile road trip, multiple super charging & level 1 / 2 charging, an OTA software update, a few touchscreen resets, used the in-car viewer, archived some "Saved" & "Sentry" files, sideloaded music & listened to same, etc.--in short, everything I could think of to use the Pi's features as well as anything I thought might interrupt power. Bottom line, the Pi ran fine, the TeslaUSB project ran fine, and the power never wavered. As far as I can tell in two weeks' observation, the 12V battery getting disconnected (or dying) is apparently the only way this power source would fail.
Code:
root@MimiPi:~# uptime
13:18:36 up 14 days, 19:34, 1 user, load average: 1.20, 1.36, 0.74
I've still got some small potatoes to deal with insofar as final placement of the wires, the Pi itself, etc. inside the center console. But, big picture: success!
