All righty then! Someone has figured it out.
We also have a book about potty training that he is very fond of...
So, we decided to get him his VERY OWN potty. After making a very big deal about a "secret, special surprise" we unveiled the molded plastic throne.
He was so excited... he knew instantly what it was. We helped him pull it out of the box, showed him how to open the lid and he climbed on it. Papa then taught him how to do the "victory dance" (climbing on top and pumping his fists, shouting "Hooray!"). The next hour was filled with much laughter, as you can imagine.
It will probably be a while before he will actual learn how to use it. But we are glad that we seized the opportunity to introduce it when we did. It's hard to deny his enthusiasm, that's for sure!