You could have the switch of your preference control a large solenoid or relay sized for the circuit you are interrupting, mounted somewhere out of sight that does the primary function of the kill circuit....

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BUT....as the design gets more complex, also need to think of fail safes or quick work arounds in case it were to fail on you..

Speaking from experience <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> , solenoids can become intermittent... failing to make contact at start up is probably more likely than failing while driving..

Having an empty fuse holder already wired in that bypasses the kill circuit might be a good idea.. If kill circuit ever fails on you (Murphy's law says this would always happen at the most inconvenient situation/time), you put a fuse in the holder to get the vehicile running quickly again until you can fix the real problem...