If you are in a 4v5 as the 4, could Zz'Rott Portal be locked to only 1 out for the other team?
Besides being complete BM if you even get it as the team with all 5 active members, but it makes wave control near impossible to manage by the 4. Having an AFK is bad enough, but also having to face a full team WITH 2-3 portals, well, you basically have no chance of winning. So why not limit the full team to only 1 active portal at a time. Multiple players can have one in inventory, but only one of them can have theirs out at a time. They would not be able to overwrite each others portals as well. So if the support places one, then until it times out or is cleared, any other teammate can't use theirs (this only applies to the team with all 5 players active).
Seriously, if you can't win a 4v5 as the 5 with just 1 portal, you should maybe look into another game besides league.