I still think this is best managed rather than coming over all officious and penalising. No one gains a benefit, it is a technical offence with no material impact, so why get on one's high horse?
Just tell 'em it's a sign of a poor pack if they can't control an uncontested ball, do they need more practice?
Yeah, it is an offence, and yes they SHOULD be able to win an UC ball without feeding or hands, and as refs we have a great affection for doing things properly. But, most players would see it as utterly irrelevant - and we are there to promote their enjoyment of the game, not to prove our own grasp of regulation and detail.
The only time I would get stroppy about it is if the ball was squeezing out of the side, and thus would have been snaffalable by the opposition - in that case, yes penalise - but if it sticks between hooker and 2nd row, which is generally because the scrum is so flaccid that the strike is feeble and no push to allow a drive over just leaves it in limbo, I have no real concern about a helpful flanker or 8 rescuing us.