Now, this may seem obvious, but not too many people realise it can be done. Okay, after you get the high jump, go down one level lower than the floor where you get the screw attack. You must have at least five missiles with you. Now go to where you would normally use the speed booster to break through the floor to reach the screw attack. Go to the far right of that room ( by the door ) and aim upwards. Now fire some missiles, and the blocks will be destroyed, opening the path to the screw attack. Now go get it.

Congrats, you've just made the rest of the game 70% easier!