"The biggest bummer though, is that it doesn't appear that you can override these limitations using JP1..."

You meant to say "yet", didn't you. I have hopes that the JP1 group will get this one figured out - and a whole lot faster than the 15-1994 was done.

Your description of Volume Lock sounds much like how it's implemented on the Philips/Magnavox REM400 (also a UEIC remote). That manual, I believe, also gives instructions that say will extend volume lock to the audio modes. It didn't work for me, but the key sequences may carry over. Heres the REM400 .pdf :
[Link: gemini-usa.com]