Fender Standard/Highway One Series Machines-Set of Four Bass Guitar Tuning Keys (0036400049)

If there wasn't some sort of sentimental value here I'd say this is a complete waste of your time - HOWEVER, first I'd plug in a cable to an amp and tap the pickups with a screwdrver or pen to see if you get a response. Use some gain so you can hear if they respond, if so, then possibly some ultra light tuners may work. Something like this https://a.co/d/0hHl8Bsi MIGHT work, but it all depends on the width of the holes in your headstock - someone much more informed and smarter than myself may be able to chime in here!