So after doing some research online, I came across this programmable tilt switch...
https://www.frederickscompany.com/pr.../0729-1736-99/
Price isn't too bad either. After contacting the company, it sounds like I can program this thing to deal with acceleration as well as tilt, in both axes.
Also, trip delay and return delay (i.e. how quickly does it disconnect the circuit after detecting the off-nominal condition, and how quickly it re-connects the circuit once back to straight and steady conditions).
It's also ruggedized enough and small enough to be mounted on the fuel tank itself, which is where the "straight and level" actually counts.
I may give this a shot at some point here in the near future.