Is there a way to make custom place mode filters?

I’m interested in adding some filters to the Place Mode panel.


For instance, if I wanted to add “Enemies” as a category to this menu and have nothing but enemies grouped under it, what would I need to do in order to add that category and set a custom object to use it?

According to this link, it appears that the Place Mode editor is completely hard-coded and the only way to add anything new to it is by editing the source for it directly. Having looked at the code for it myself, I’d come to the same conclusion but hoped that I was hallucinating.