REMOVE BANNER OF COMMAND FROM URF(CAN BE ABUSED)

I was in an URF with a couple of my friends and as we were playing we noticed that there was a lot of zzrots coming out of the enemies base. Then as we got in we noticed that they had blocked off the middle lane minions and putting banner of command on each one of them. They then released all the minions at the same time. As the game went on we could not kill all the minions in time because they were invulnerable and they pushed all the way from their base to ours and we lost.