How about making a rule about late report, as it was in FB. I mean, when player A wins vs player B in scheme X, but then doesnt report and player B plays vs player C in same scheme and reports his win, then later report of player A shouldnt be allowed, because it will affect rating in other way than it would if game was reported just after getting finished. In FB it was solved pretty nicely: 1h time to report and later you can report only if opponent didnt play games in this scheme.
Just a suggestion of course.