Yeah, I suppose I could do that. I'd have to experiment a bit to get the weight just right, and I'd have to polish the outer surface of the weight so it didn't tear up the plastic as I was pressing it back in, but that wouldn't be too hard.
I was hoping to make something were I could press the old weight out and a new one in just by putting the slider into boiling water to expand the metal tube, then putting the slider into a Dake press. In that way, I could experiment with different weights to find the best one, without having to remove the plastic each time.
Another idea I had was to make a rubber stopper arrangement, with an identical weight on each side of the stopper. It'd have a bolt going through it, with a union nut on the other side with a head on it. Tighten the bolt, it squeezes the rubber stopper, and locks the weight into place inside the metal tube. To put a different weight in, just loosen the bolt, remove the assembly from the metal tube, unscrew the bolt from the union nut, slide off the old weights, slide on the new ones, and reassemble.