You have to have gone far enough to get the Ice beam. Now go to the room where the bridge needs to be formed and there's the statues of Ridley and Kraid. Before you enter that room, have the winged enemy chase you and hit you as you are going through the door.

If done correctly, the enemy follows you into the next room. Simply freeze him and use him as a stepping stone to get across the gap - without beating Ridley or Kraid. You can theoretically beat the game in under 20 minutes by using this glitch.