Best way to corkscrew 540 is to throw your arms and head in a rainbow motion to your side, rather than around your waist when you spin. I.e. when spinning left Drop your left shoulder and throw your head towards your left hip. Your Right arm should go over your head and your left hand around the back of your waist (Do the opposite when spinning right). You are aiming to tilt your head so that it is upside down, without having to take your eyes off the direction you are travelling. Your legs should come over your head from the momentum of the ramps transition. If you have got the spin right, landing will be easier than a normal 540.

Note: This technique only really works for people who spin the opposite way to whichever way they look over there shoulder when going fakie, i.e. I naturally spin left and look over my right shoulder when going fakie, which makes 540's a lot easier.

 If you want to go one better with a cork 720, throw harder, then as you reach 540 whip your head in the direction you are spinning and towards the ground to spot your landing forward.

Hope these tips help