If you're using SimpleGame (which can probably be considered a game for testing) you're using a FirstPersonHandler, which has a MouseLookHandler to handle mouse look.
If you want to require a button to be pressed while moving the camera you could try this in your simpleInitGame():
//Require a button press to move the camera
((FirstPersonHandler)input).setButtonPressRequired(true);
//Set button to right mouse button
((FirstPersonHandler)input).getMouseLookHandler().getMouseLook().setMouseButtonForRequired(1);
If you want to do it the other way around...perhaps you could set your own MouseLookHandler with your own MouseLook class that implements the following edited method instead of the normal one (a very minor change):
/**
* <code>performAction</code> checks for any movement of the mouse, and
* calls the appropriate method to alter the camera's orientation when
* applicable.
*
* @see com.jme.input.action.MouseInputAction#performAction(InputActionEvent)
*/
public void performAction(InputActionEvent evt) {
float time = 0.01f * speed;
Also setting the above variables.
It might also be an idea to switch to extending BaseGame yourself or using StandardGame with GameState's.
Then you can implement only the parts that you want in your game the way you want them.