Credit goes to this video, here are the steps which are also in the video description:
Step 1: Get you and 2 people in a lobby
Step 2: Invite your friend(F1)
Step 3: Have another friend(F2) get ready to join your lobby
Step 4: Make sure (F1) Match makes to another lobby before Joining. (Makes Glitch Work Better)
Step 5: When your friend (F1) is at 70% loading, kick him
Step 6: Once you kick your friend (F1), friend (F2) needs to join your game right away.
Step 7: If you did this right, you should have at total of 5 people in your lobby.
Step 8: Tell Friend on the Team with him only in it to invite others for 8 People.
Step 9: Repeat Steps for More Players & ENJOY