Plugged the flat tire and pumped it up. Seems to be holding pressure. I hope it's okay, they're Michelins, not even a year old.
Also bought a proper x-form lug wrench and found a 3' piece of pipe just the right diameter to use as an OOOMPH! with the wrench. Tried to remove one of the lug nuts on the tire that's now on the axle. The pipe was needed to get enough leverage...
I appreciate the guy who replaced the tire, but apparently he didn't understand that "proper torque" doesn't mean "tighten until you'd need Superman to loosen it."