Let's combine this with the zip file approach. Your app is distributed as a zip file containing only the app folder. Safari unzips it automatically, then the user double-clicks your app icon. Your app notices it's in the "Downloads" directory and asks "Would you like to install me to the Applications folder?" If so, the move is done visually by opening two finder windows and literally moving the app icon as if it was being dragged. Afterward the Applications folder remains open displaying the app icon in case the user wants to drag it to the dock.