Inspired by the experiments Hiroshi Tachibana made with a recorder (check this post), I decided to try something with a regular whistle. It is a success, and it took me less than a quarter of an hour!
I just took a regular brass whistle and filed it with a half-round file. Then, when the hole was done, I buffed the edges. Done!
Here is a sound sample : the sound is a bit "windy" because the labium window is wide, but the instrument is funny and really playable :