I don't know how, but my dad has some way of dipping his tool handles into liquid rubber so he can put rubber grips on his wrenches and hammers and so forth. That's a great thing too, because it gives a better grip than the bare metal.
I don't know how he does it, but if you can find that liquid rubber stuff you could probably dip the nub into it and give it a rubber coating. Baring that, you might also just cut a small piece off a latex glove and wrap it over the nub and secure it in place with either a twist-tie or a rubber band. It would certainly look like crap, but it might get the job down at least.
Those are just a few suggestions. I don't know if either of them will work or not, but you could give them a shot.