No 914 that I'm aware of ever had a dead pedal in it from the factory. There are a number of aftermarket ones available, even the stock 911 that Mark posted above.
If you're interested in it being truly invisible, have one like those welded in, then modify your carpet to fit over it. Then glue on a pedal cover of some kind--I wouldn't use a brake or clutch pedal cover, because they are smaller than I would prefer for a dead pedal. But I might try cutting down a big "double wide" brake pedal cover from some 70s land barge and using it, or perhaps cutting up an old accelerator pedal and using that.
Failing that, get whatever you like and paint it black. It'll disappear under the dash anyway.
--DD