Overriding the toString() method of the object you put into the tree node is certainly the most natural way to do that, and I can't really see why you would not want to do it. But if there is some reason why not, you could probably have your TreeCellRenderer set some different text.
Hey cool! They got a blimp! But I have a tiny ad:
a bit of art, as a gift, that will fit in a stocking