The BlackBerry® 10 Dev Alpha Simulator in portrait mode requires switching focus between the Virtual Machine and the host OS to interact with scroll bars.
Use the BlackBerry Simulator Controller to adjust the simulator zoom level.
You can run the Controller by executing the controller file located in the controllers sub directory, which can be found within the simulator installation directory. Once you have it up and running alongside the simulator, click on the Connection menu, choose Connect and enter the IP address of the simulator. After it has connected click on the View menu, choose Change Zoom Level and adjust the zoom value so that the simulator fits on your screen.