I think you'll find that the pin that is pushing up out of the top of the die is the rod that the expander ball is formed from and has the decapping pin pressure fitted into the tip.
But, as you say, if you have the tools and some materials to start with you can fashion an expander and replace the factory one. Or, cut / extract the decapping pin from the tip of the one you have, and order a replacement - shouldn't cost more than a few $$.
Just a Shooter