im not to sure im trying to work it all out myself now but as i mentioned before would steel wool do the trick
the only way i can think it would work is say you have the inlet and outlet next to each other and have a partition/baffle in between made from fine steel wool so its like divided into 2 tanks inside by the steel wool so air and oil go in one side and just air comes out the other because the steel wool has caught the oil on the way through