I agree that our transitional phases could be a lot smoother Manc, but in reality I don't think bringing in an assaistant as a sort of apprentice is a practical approach. For starters, managers like to have their own people around them, and anyone coming in would probably feel a little undermined to have to serve under a predecessor (albeit one as experienced as Broon) before taking over for themselves.
To be honest, McGhee could've been phased in over five years, worked his way up through any number of roles or parachuted into the centre-circle half an hour before kick-off against Sigma; he'd still have been an unmitigated pile of horseshite. More worthwhile putting in the hours before Brown's inevitable departure to find a manager who'd be a good fit for the club. And who won't take every fucker back when defending corners.
Edit: Good points too BTR. Although, with such increased player turnover, even more caution should be taken when dealing with managers, lest we end up in some perpetual whirlpool of 'transition' where managers and playing staff don't stick around long enough to put a run of 38 decent games together.