Hicks put the egg on Sulaco. Bishop was busy with....spaceship stuff.....and Hicks jogged down, clamped the egg shut with his hands and brought it to the ship. Then he got sedated by ol Bishop. He woke back up while Ripley was in the shower and stuffed it wherever. He was in on it the whole time. It's why he was so eager to grease Burke. Heck, Burke was telling the truth. Hicks dumped the facehuggers out, but had to help kill them once the attack was revealed to keep cover. lol.