AFK Detection Idea

So I have played a lot of games where people know that you can get banned if you do not move at the base for five minutes so they will stay in the base and type and move around in the base to make it seem like they are actually playing the game. Yes, they can still get reported by players for Leaving the game or AFK, but I think something that Riot could do (if they do not already do this) is have a timer of how long someone has spent total in the base (not time dead, but once they have spawned, how much time they have spent in the base). Now, instead of giving them a warning to leave the base (since they could just leave the base and walk around the Nexus) do not warn them at all. At the end of the game if a certain players time in base is significantly longer than the others, then he was probably AFK.