Here is my trick to build any bladder shock.
Fill with oil with the rod fully extended then slowly cycle the rod in and out. You will see air bubbles form. Let the shock set until the bubbles are gone. It helps to have a shock stand to do this as it takes a few minutes.
Make sure that the oil is up to the top of the body with the rod extended then put the bladder in place on the body. The bladder should force out a little oil.
Put the shock cap on a few turns and compress the shock. This will push out some more excess oil.
Tighten the cap full and clean up the mess. If you do this right you will have a little rebound and a smooth air free shock.
If you have too much rebound loosen the cap and force out a little oil.
If you don't have any you will need to remove the cap, add some oil and repeat the bleed.
Good luck, there is a definite feel to this technique but with time you will build perfect shocks.