PoC, I've had some limited experience in designing products for those with special needs but have a couple of initial suggestions:

- If you lack the sensory feedback needed to half-hole accidentals then perhaps using a crossfingering technique may help - the vast majority of notes are either open or closed.

- You could instal barriers along your whistle to encourage your fingers to move to the right spots. Just for starters you might try clipping the lightweight PVC hose clamps used in plastic irrigation pipes - the type with the compression ratchet closure. They're common in hardeare shops here, and presumably elsewhere around the world. The commonest size is meant for 13mm pipe but should work on the larger diameter whistles. If it actually works, you'd need seven of them.

Regards, John