netem can be used to introduce delay, but it requires enough memory to store the data for the full delay, so depending on link speed and router memory this might or might not work. I think @dlakelan in the past actually had a script that allowed to set up netem delay to help gamers. However keep in mind that gamers tend to try to game everything, so some folks add delay to get graded by the server and then strategically disable the artificial added delay to gain an unfair advantage over their opponents... and that is why we can't have nice things... 
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