Slide whistles are available with at least 2.5 octave ranges. Procure one, and attach a dowel or ruler to the side of it in a way that does not interfere with the slide action. Marks or tapes may then be placed on the dowel, and the doubled back end of the slide can be moved using the tapes for guides. In order to see what you're playing, I recommend stretching a length of flexible plastic tube from the mouthpiece of the slide. Because the slide whistle has a recorder-like mouthpiece and it doesn't really matter whether your lips are on it or not as long as an airtight seal is formed, you can use this device to move your head wherever it's comfortable.