Thank you for the tips.
I tried other systems, and different USB ports on those systems, without any luck. I also used the intriguing "Windows Enabler" tool, but it too was unsuccessful at enabling the update button.
I have managed to find someone with the v1 prs-500 CD. I am going to try and load that when I get it to see if I can downgrade or re-flash my unit.
I'd hate to throw the little guy in the trash, but I can only imagine what Sony charges for an out-of-warranty repair. I understood the risk, but I should have never attempted the UF. Period.
To those out there across the interwebs - this is an example of an unrecoverable, truly bricked, Sony eReader after running the Universal Flasher.