While in instant-replay screen hold R1 or L1 and your players shadow will start to move around.

While playing press start and go to Team management option and go to substitution menu. Pick the character you want to double or triple. After you pick him, put him at the Bench. Press ok button. Then unpause the game and wait for the substitution.

After the substitution is complete, go to the substitution menu again, replace ONE character with your chosen character press cancel, then go to the substitution again. This time you'll see that your chosen character still remains on the bench. Choose another character and replace with your chosen character. You can do this over and over. After you finish changing character, unpause the game, and see the substitution!