I found this accidentally a long time ago and have used it for a very small advantage during games since. This method will mask your runes and masteries from people that use lolnexus to scout games. After the countdown timer there's a sound clip that plays. After the clip plays is the time frame you have to swap your rune page and hit edit for masteries. If done correctly, your rune/mastery bonuses will still be there, but invisible to lolnexus.