Might as well use the bot idea for rooms that was tried some time ago(like half a year if i recall correctly).It gave the ranking for each player in each official room.It was given a test,but I don't recall why it never stayed permanently.Maybe because they we're working on the current ranking system,and found that it would be a much better idea.

If we want to apply your idea,then we're doing it to prevent the farming that might happen for the global and mod ranking.So,we would be solving one problem which is the mod ranking.The global ranking would still be flawed.So,why not work on a solution that would guarantee the correct functioning of both systems?