Maybe not Cup games, but I think players like Cleary and Luai played a season or 2 in the under 20's comp at the time. I am hoping Mozer is as good as everyone here thinks he is, but he can wait another 12-18 months, instead of us forcibly ruining a good thing because we're scared of losing him. A lot of examples of teams changing what works for potential and it all ending horribly (us included).
If we really want him to get some experience, we should loan him to someone for a season (works well for players like Arthars and Grant).