The right way to fix this is to get the right hex key and make the adjustment, as your posting implies you already considered. I don't know what the right size hex key is (assuming you have checked out that the correct tool is a hex key and not, say, some kind of screwdriver). I would recommend buying a set of small size hex keys from the hardware store; I almost never see them sold individually. One of them should be the right size.
If you don't want to buy hex keys, think about sticking some kind of plastic or thin foam strip onto the top of the lift beam, where it would touch the tonearm when you go to lift it. Several layers of thick tape, cut to the right size and shape could do the trick. The only potential problem with this is that your lift piston could be loose, so it would continue to sink over time, and you could wind up adding more and more tape.
If your lift piston is in fact a little loose, you could try gently pushing up on it from below with a finger, hopefully recovering the slipped vertical distance that way. Still, I would get the right hex key and tighten it down eventually. Good luck.
If you don't want to buy hex keys, think about sticking some kind of plastic or thin foam strip onto the top of the lift beam, where it would touch the tonearm when you go to lift it. Several layers of thick tape, cut to the right size and shape could do the trick. The only potential problem with this is that your lift piston could be loose, so it would continue to sink over time, and you could wind up adding more and more tape.
If your lift piston is in fact a little loose, you could try gently pushing up on it from below with a finger, hopefully recovering the slipped vertical distance that way. Still, I would get the right hex key and tighten it down eventually. Good luck.