The solution is easy but won't happen. You simply start imposing serious penalties for cheating and bad sportsmanship and it will stop. But that requires enforcement. In one of our sectional tournaments, a young lady refused to call out the score even after multiple warnings from the linesman . . . why? b/c she cheats on the score by not calling it and then calling a wrong score in her favor. Finally, she had to default the match in the 3rd set after she told the judge "I don't have to call the score" . . . are kidding me! That wasn't enough of a penalty. That's an instance when the kid should be suspended for at least 3 months (maybe 6 months).
Another solution . . . ban parents (I'm dead serious). My son is a competitively ranked chess parent. Guess what? Parents aren't allowed. Parents can watch in a room where they have split screens showing matches but you can be there up close.
I just wonder . . . what would happen if parents could only watch on a big screen in a meeting room and no parent was allowed to sit on the fence? Now, it's just kid vs. kid . . . funny thing, kids seems to work things out . . . cheating is taught and generally the kid cheats b/c they want to win so bad but not for themselves but to win to keep their parents happy . . . they connect the win with love from the parents (that's the saddest part).