With a little bit of creative tinkering, you can turn one of those failed glass bowl pumps into a dummy, and use an electric pump with an oil pressure operated failsafe system to actually supply the gas. Hide the electric pump back under the cab where it will be hard to see.
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!