Unfortunately, that doesn't do it. For example, when I load a saved tournament, the "Tournament Loaded" dialog opens on the extended display. Doesn't matter how many times I drag it back to the main display. It always appears over there.
So I did what you recommended, then started TD, loaded a saved tourney, and no dialog. I click on the tourney setting screens and get the "bonk" because it is waiting for me to click OK. I turned extended display back on and there it is, floating on that second screen.