first you must have a friend (who is a priest) of the oposing faction.
ask them on vent or the phone, to mind controll you just as the other team is about to win
for example a horde guy mc's you while horde are on 1990.
when the game finishes the server will still recognise you as MC and on the oposing faction and will give you 3 marks as it thinks you were on the winning side.
as a little add on, you can use your MC cap right before the game ends and make the oposing teams member only get 1 mark.