Okay yeah it was what I understood and yes It will take a few time but nevermind (posting random result is fairly quick
)
Anyway IMHO you should use something very similar to what Kael post when the paring are announced with a third collumn with the title : bet.
like this :
Opponents bet
player1 vs player2 I bet player...
Then every one can edit himself his/her sheet, for example changing colour of his bet (red if he/her was wrong, green if right)
Then warmaster or any admin/modo can check and count easily then report all the result in a big sheet with all the participant.
Thouhgt ? Maybe we can't let every one editing his own sheet.. But if it is an other personn who do this It will be a lot of work !