So all the design needs is a little light to tell you to keep driving around and avoid hills when the aux. battery level is low.
.. or a handle between the seats.
... or use your left foot
I still don't see how that would work in a manual.
Left foot on clutch, right on the noisy pedal. Find the bite point and pull the handle on the dash that disengages the "handbrake".
The two downsides (on the merc van I was using at the time) were that it was binary, so if you didn't have enough bite on to hold the van, you'd better get on it quick as you're rolling backwards
. And it made a lout "pang" noise when it disengaged.
Not as good as a proper handbrake on a manual car imo, but fine on an auto.