very difficult question, I can sing in the whistle register, but it took me two months to master it...and I'm still trying to work on the passagio from the head. It's like anything else really, so long as it doesn't hurt you're not raising your larinx, and it's free you should be ok, It's a completely different sensation to other registers the throat feels..err, small, but obviously that's the vocal chords, as they zip up. there's no feeling of reaching for the notes, in fact the harder you try, the harder it is, one of the stepping stones for me was realising how easy it was, rather than thinking "my god it's high" I started off with the breath controll (like trying to blow a feather from the palm of your hand) which is a good tester as to wether you are doing it right or not, then on to 'meaowing like a kitten or squeacking like a mouse, then putting that sound into a continuous note. It will take time and practise, it's hard not to force the larinx up and strain your voice, which i suppose is the main reason alot of teachers won't teach it. It is more of a mind over matter approach. perhaps the lip rolls excersize might help you. sorry haven't heard of the 'cuperto technique' I might just toddle off and look that up!

A lot of experienced and professional vocalists have mentioned that singing in whistle register is not quite something you can practise and get right and then you are labelled a 'whistle register singer'. It is believed that only a few coloratura sopranos and and other sopranos(like spinto) who can hit notes in the seventh octave are the real whistle register singers. I believe that people should stop trying hard and hard to get there, I just see it as a rare gift. Not that Im dicouraging people out there, Im just sharing a thought. TT

http://ca.youtube.com/watch?v=yftMw57h3B8

I will try to upload the vid. hold on.