Off Button?

Suitable switches exist, it sounds like you want a "make before break" (no pops) latching (not momentary) pushbutton switch. Would be easier to find a standard toggle switch through.

 

I haven't heard of one on a bass, but they are not too uncommon on guitar.
http://www.instructables.com/id/Guitar-Killswitch-Strat.-design/

 

Seems like a bunch of work for something most tuner pedals do. .02

 

my friend had one of these put on his guitar, so it's probably not unusual. I would ask your local repairs shop.

looks like you can get pots with them built in, too, which might be a good non-destructive way of doing it (i.e. no drilling involved):

Shadow SH124-500 Kill Pot

 

except if you want to play Tom Morello-style rhythms with it! my feet aren't that fast...

 

Ahhh touche

I love how creativity reaches so far beyond jus making notes on an instrument.

 

It's called a killswitch and it's a fairly common mod on electric guitars. Any MOMENTARY*, normally open pushbutton should work. The switch is installed in parallel to the output jack, pushing the button down grounds the output and silences the bass. Some people like the big "arcade game" style pushbutton.

 

How 'bout one of these...
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