itween path restrict rotation on TWO axis

I have a camera following an itween path (using "MoveTo") which is oriented to its own direction (using "orienttopath"). I would like to restrict the camera rotation on only 2 axis, x and y, leaving z rotation controlled by the user. Is this possible? In the itween documentation i found the command "axis" to restrict rotation on only 1 axis but i would like to restrict it on 2 axis! how can i do? i tried to duplicate the itween path script and restrict one to x and the other to y and give them both to the camera, but it doesn't work: the camera rotation is again restricted on only one axis. Can you help me? Thanks very much!