I have a hall light which is wired as a two-way with the landing switch. The hall light has three switches although only one is used. They all have C, L1 and L2. I wish to run an outside light via a cable which is already installed (from within the hall switch box to the light ouside) although not connected. Is there a way in which I can take power from the connected switch to one of the unused switches to save any rewiring withing the walls etc? By the way, the two way landing/hall light has a dimmer switch in the hall and a normal switch in the landing. 
