I've done some tests while integrating the new Google Play Games with fake scores, now I need to reset the leaderboards before publishing my game!
I found this REST API: https://developers.google.com/games/services/management/api/?hl=en#Scores
But this seems to be related only to web games, not Android games: "Use the Google Play game services REST API to set and retrieve game services data from your web game"
Thanks!