CRTL and left click to tilt camera

I have added keyboard controls to my application all of which work perfectly fine. The camera tutorial proved very helpful but what I would also like to achieve is to be able to add a tilt function that is used when holding down the CTRL key and left mouse button and moving in the direction needed. Is this possible? This would help for laptop users where in most cases there isn't a middle mouse button to tilt the camera.

I am currently looking at the source code on my machine at the rotateHandler but my application isn't pointing towards the source files on my machine I don't think. Could somebody also tell me where this is defined? Thanks in advance.