Since the online is pretty dead and if you do get someone who will actually play you, they're likely to be using a chess calculator, the best way to do this is to boost with a friend. Starting a game and having the other person resign has had mixed results so the best way to do it is to do a Fool's Mate so you can achieve checkmate in the fewest amount of turns.
Challenge your boosting partner to a game and make the following moves (black to win).
1. Pawn to f3 : Pawn to e5
2. Pawn to g4: Queen to h4
Then do the reverse for the other person. If you need white to win you can do it in one extra turn like so:
1. Pawn to e4: Pawn to f6
2. Pawn to d3: Pawn to g5
3. Queen to h5