A simple manual selector valve for multiple fuel tanks could be set up that way- - - -providing fuel input to the mechanical pump in one position and to the electric pump the other way. Most of those valves are designed to mount under the floorboard with the selector handle accessible to the driver under the seat. Some valves have an "off" position which could act as an effective anti-theft device.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!