I know you don't
want to run a vacuum shutoff, but I continue to believe that that is the most straightforward and trouble-free solution to your problem.
One option is to get something like a Ford electric vacuum pump and just wire it to a momentary switch in the cab. It only runs during the very short shutdown cycle.
If it happens to have a check valve so vacuum remains in the line after shutdown, just take a hot needle and poke a tiny hole in the nylon vacuum line so the vacuum will bleed down within 2 seconds. Then just wrap it with some filter material and put a bit of shrink wrap around it and shrink one end to hold it in place.
On a good day with a half off sale, you could probably source a pump at the junk yard for $5.
I'm running a manual shutdown in my project and I'm quite happy.