There were a post couple days ago by the dude who's making the bagel game (or something like this, Lou iirc). He asked about the same thing. The only way to do this is basically validate the data with a hash.
For example, you send 3 infos on the json: player_name, plays and score. By having another info, lets say, checksum, you can validate on server side if the 3 info matches the checksum.
For the checksum you can use kyatric's hash plugin and maybe use SALT+PLAYER_NAME+PLAYS+SCORE, having the salt being know both by the game and the server.
Actually, theres another way: to compute the score on server or basically simulating if the score is achievable.
This concern/problem is not a construct specific thing; the problem here is the ease for users to see/change the values.