Bend your knees a lot and use your arms loads, make sure you time the rotation if your chest and pecs with the launch as well as the raising if your arms with the extension of your knees.

If this isn't enough then try this to get you started:
-open xspar in singleplayer.
-in the first turnframe hold all, lower shoulders, relax knees and bring them up toward your body using the hips (so both feet lift off ground).
-in the second turnframe contract knees and lower legs with hips (not sure if it is extend or contract for this). You should land on the ground kneeling down.
- then lean forward a little and extend knees while rotating chest and pecs. Experiment with this frame watching what your ghost does, try holding or relaxing the legs separately rather than symmetrically.
-work on how you move in the air and on landing.

Then once you have done this open up xspar again with a new game.
-start with a run.
-try to sink down onto your knees while letting your arms lower so you are in a similar position to the one you practiced (but without the knees touching ground or your feet living off the floor).
-try to launch the way you practiced to get a cork.

Then just keep working at making the launcher smoother and more subtle.

I hope this advice helps.
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I just realise that what I suggested wasn't really a cork at all since it doesn't flow. Nevertheless try what I suggested and get into a habit of using your chest at the right time. Then try to do it with one leg and then try to bend the knees less and less to add subtlety.

I feel like a moron.