Some guys already use this strategy in the cup, it is long term strategy. The best way to decrease avQ is to keep few (at least 4) 0T academy players in team (as reserves). Instead of improving them by adding SP to skills, you should train special ability or new position for that player to spend SP. That is better than saving skill points because you could auto add them by accident. More promotions you get, more influence would they take to the stars average.
2 seasons ago I've faced such opponent in the cup (1 level above me), his 1st team had 7* players and 1* players (according to my level). He lost the cup finals against team which had 9* players and 1* players, but whose avQ was equal as mine.
It is unfair strategy, but the cup is unfair competition by default, so...