OK I've stumbled upon a perfect workflow by accident! I had one of the Leicas to set to shoot DNG only, not DNG+JPG. When I do command-E in PMP and edit in C1, and export to the same folder as the original, PMP picks up the new JPEG and shows it with the original DNG as a DNG+jpg (I have set lowercase extensions in PMP) and selects the new JPEG for preview! So it immediately interactively shows the results of C1 adjustments.
Now the only problem is when the original camera ingest brings in pairs DNG+JPG. My current manual solution is to select the shot, ctrl-click it, Reveal in Finder, and move the JPG aside to ... 0.JPG. Then cmd-E / cmd-L / cmd-D creates an adjusted .jpg that, back in PMP, is paired with the original DNG.
How can I automate it, moving the original JPG if it exists away to ... 0.JPG?
Alternatively, I can instruct C1 to overwrite the existing JPG, which I back up anyways. Still I wonder how can I move it aside instead.