maachuu,
Not DoubleG but I can answer the question for him: Yes you can but you must do so while in the forced Simulator mode and not in the normal Simulator mode that the unit will automatically go to when powered on without a transducer being connected. To get into the forced Simulator mode:
1. Power the unit on as you would normally do.
2. While the unit is displaying the title screen (will be showing something like: “Humminbird 997c Si”); press the MENU button and allow the unit to continue to start up.
3. The display should change to show three or four menu options (depending on the unit and software version you are running), one of which is “Simulator”.
4. Use the Up and Down Arrow buttons and finally the Right Arrow button to select “Simulator”. After a few moments the unit will start showing simulated sonar and GPS data.

The differences between the (Point Of Sale) Simulator mode and the forced Simulator mode are that the POS Simulator mode does not remember any menu or setting changes and will reset them all about two minutes after the last button press. It was designed for use as a Point Of Sale Simulator for in store use. The forced Simulator mode was added so that users could make and save menu changes as well as changes to their waypoints, tracks and routes.

Just a caution here: what may look to be the best settings for the simulator sonar may not be the best for the water you will be using it on. So you may still have to tweak it a little bit. The simulator will allow you to become more familiar with the changes you will see when you adjust a menu item though, so practice until you are familiar with the menus.