Very valid point about the verbal versus visual cue! Nele does respond to either on this trick, but that is an exception. He very much prefers visual cues. Sorry jmlw, I should have taken this into account in my first post.
I didn't have a training perch at the time we trained the trick, hence the hand. Although, as soon as he understood the trick he could translate it to any surface he was on.
I keep the treat at beak level for him when luring. This was partly because I had never trained, or read about training, a bird... and partly because he wouldn't have been 100% comfortable with a hand above his head when we started this trick... it was also influenced by the fact that Nele is a bit unco, and keeps his head down for balance while turning (and uses his beak to balance if he is on a perch, even when he is turning by himself without human intervention).
I class a hand above the head as something I would do with a bird that already trusts me, unless I was specifically using turn around as a way to get a bird used to my hand above it's head. Please note; I am not an expert! This is based only on my interpretation of the ringneck logic I've seen so far. My practical experience is limited to what Nele has vouchsafed to me

Sorry, there is probably too much personal philosophy in the post to make it valid now ;p
jml: Did you find a favourite treat for Remy?
If you are still not finding any motivation on his part for the trick, target training could be a viable option... I'm afraid I can't help there, we skipped that lesson..
Claire