Well, I tried it. CDMAGE didn't want to read DDR Club Mix (it wouldn't recognize it as a valid .CDI image), but it did read it as RAW and I extracted the files from both sessions.
I then tried Echelon's method, and every other utility I could find, and added several coasters to my collection.
Finally, as a "what's one more frisbee on the pile" act of curiosity, I tried it in DiscJuggler 4.0 one more time -- this time setting the Mode for unrecognized images to Mode 2, TOC to CD-XA, selecting RAW write and selecting Overburn CD, along with the previously-selected Add post-gap option.
And it worked. Go figure.
Maybe I'll go back and try the method with my DDR 2nd Mix CDI, which I only got working in a non-self-boot config. Anyway, thanks for the advice...
(If nothing else, I can extract the audio tracks and burn an audio CD.)