Fear not, for the antidote to atonal antics is here!
The autotune slide whistle, an invention the musical world has been crying out for, is simply an ordinary slide whistle, but with a plastic thingy attached (blue). A semi-rigid tab (green) snaps into the plastic thingy, locking the lever to concert pitch.
The tab could be turned to re-enable the portamento, or perhaps the handle could be flexible enough that a simple deflection could temporarily bring back the sweeping effect during a performance.
Unlike many of the concepts on this site, this one could quite easily be implemented in real life! Without too much difficulty!
The plywood was cut first, then the magnet mounted to the plunger with superglue, and finally the positions were marked out in pencil before drilling the holes, glueing in the magnets, and covering it in tape to provide a smooth surface.
You might wonder why the positions are somewhat erratic, instead of a straight logarithmic progression. This is because the airflow required (how hard you must blow) is different for different notes. Blowing harder moves the anti-node so the wavelength becomes shorter. Or perhaps I was just inaccurate with the positioning. It sounds reasonably in tune, though.
(Update again) To see the Autotune Slide Whistle in action, check out the video I posted for the MIDI slide whistle.