I've managed this playing with two controllers on the same team and with a bunch of computers playing on the highest difficulty.
To complete without a second controller start a local game and place a team of computer players against noone and set the computer difficulty to full. I managed to see at least 3 Alley Oops in the first round alone.
With two controllers you need one on the small white platform between the goal and ball and the other player to stand with the ball on the grey block to the side of the balls starting position.
Have the white platform guy jump up high and then press x to pass the ball with the stationary player and x again with the jumping controller as soon as the ball is caught.
I managed 3 out of 4 goals to be alley oops with the 4th one pressing too late and landing before the shot was taken.