I play sackpipa a bit and when I want to practice tunes in the minor scale of the chanter without picking up the pipes I use a whistle with the second hole from the top half covered in tape or blu tac.
A tune that goes great on keyless flute is
https://m.youtube.com/watch?v=6Y1oKFR24tI
Lots of free tune books and resources for sackpipa on the web. Any tune in the major mode will work fine on a keyless flute.